The Internet Domain Name System (DNS) consists of the syntax to specify
the names of entities in the Internet in a hierarchical manner, the
rules used for delegating authority over names, and the system
implementation that actually maps names to Internet addresses. DNS data
is maintained in a group of distributed hierarchical databases.
The Berkeley Internet Name Domain (BIND) implements a domain name server
for a number of operating systems. This document provides basic
information about the installation and care of the Internet Systems
Consortium (ISC) BIND version 9 software package for system
administrators.
In this document, Chapter 1 introduces the basic DNS and BIND
concepts. Chapter 2 describes resource requirements for running BIND
in various environments. Information in Chapter 3 is task-oriented
in its presentation and is organized functionally, to aid in the process
of installing the BIND 9 software. The task-oriented section is followed
by Chapter 4, which is organized as a reference manual to aid in the ongoing
maintenance of the software. Chapter 5 contains more advanced concepts that
the system administrator may need for implementing certain options. Chapter 6
addresses security considerations, and Chapter 7 contains troubleshooting help.
The main body of the document is followed by several appendices which contain
useful reference information, such as a bibliography and historic
information related to BIND and the Domain Name System.
This document explains the installation and upkeep
of the BIND (Berkeley Internet Name Domain) software package. We
begin by reviewing the fundamentals of the Domain Name System (DNS) as
they relate to BIND.
The Domain Name System (DNS) is a hierarchical, distributed database. It
stores information for mapping Internet host names to IP addresses and
vice versa, mail routing information, and other data used by Internet
applications.
Clients look up information in the DNS by calling a resolver library,
which sends queries to one or more name servers and interprets the
responses. The BIND 9 software distribution contains a name server,
named, and a set of associated tools.
The data stored in the DNS is identified by domain names that are
organized as a tree according to organizational or administrative
boundaries. Each node of the tree, called a domain, is given a label.
The domain name of the node is the concatenation of all the labels on
the path from the node to the root node. This is represented in
written form as a string of labels listed from right to left and
separated by dots. A label need only be unique within its parent domain.
For example, a domain name for a host at the company Example, Inc.
could be ourhost.example.com, where com is the top-level domain
to which ourhost.example.com belongs, example is a subdomain of
com, and ourhost is the name of the host.
For administrative purposes, the name space is partitioned into areas
called zones, each starting at a node and extending down to the “leaf”
nodes or to nodes where other zones start. The data for each zone is
stored in a name server, which answers queries about the zone using
the DNS protocol.
The data associated with each domain name is stored in the form of
resource records (RRs). Some of the supported resource record types
are described in Types of Resource Records and When to Use Them.
For more detailed information about the design of the DNS and the DNS
protocol, please refer to the standards documents listed in Requests for Comment (RFCs).
To properly operate a name server, it is important to understand the
difference between a zone and a domain.
As stated previously, a zone is a point of delegation in the DNS tree. A
zone consists of those contiguous parts of the domain tree for which a
name server has complete information and over which it has authority. It
contains all domain names from a certain point downward in the domain
tree except those which are delegated to other zones. A delegation point
is marked by one or more NS records in the parent zone, which should
be matched by equivalent NS records at the root of the delegated zone.
For instance, consider the example.com domain, which includes names
such as host.aaa.example.com and host.bbb.example.com, even
though the example.com zone includes only delegations for the
aaa.example.com and bbb.example.com zones. A zone can map
exactly to a single domain, but could also include only part of a
domain, the rest of which could be delegated to other name servers.
Every name in the DNS tree is a domain, even if it is terminal, that
is, has no subdomains. Every subdomain is a domain and every domain
except the root is also a subdomain. The terminology is not intuitive
and we suggest reading RFC 1033, RFC 1034, and RFC 1035 to gain a complete
understanding of this difficult and subtle topic.
Though BIND 9 is called a “domain name server,” it deals primarily in
terms of zones. The primary and secondary declarations in the named.conf
file specify zones, not domains. When BIND asks some other site if it is
willing to be a secondary server for a domain, it is actually asking
for secondary service for some collection of zones.
Each zone is served by at least one authoritative name server, which
contains the complete data for the zone. To make the DNS tolerant of
server and network failures, most zones have two or more authoritative
servers, on different networks.
Responses from authoritative servers have the “authoritative answer”
(AA) bit set in the response packets. This makes them easy to identify
when debugging DNS configurations using tools like dig (Diagnostic Tools).
The authoritative server, where the main copy of the zone data is
maintained, is called the primary (formerly master) server, or simply the
primary. Typically it loads the zone contents from some local file
edited by humans or perhaps generated mechanically from some other local
file which is edited by humans. This file is called the zone file or
master file.
In some cases, however, the master file may not be edited by humans at
all, but may instead be the result of dynamic update operations.
The other authoritative servers, the secondary servers (formerly known as
slave servers) load the zone contents from another server using a
replication process known as a zone transfer. Typically the data is
transferred directly from the primary, but it is also possible to
transfer it from another secondary. In other words, a secondary server may
itself act as a primary to a subordinate secondary server.
Periodically, the secondary server must send a refresh query to determine
whether the zone contents have been updated. This is done by sending a
query for the zone’s Start of Authority (SOA) record and checking whether the SERIAL field
has been updated; if so, a new transfer request is initiated. The timing
of these refresh queries is controlled by the SOA REFRESH and RETRY
fields, but can be overridden with the max-refresh-time,
min-refresh-time, max-retry-time, and min-retry-time
options.
If the zone data cannot be updated within the time specified by the SOA
EXPIRE option (up to a hard-coded maximum of 24 weeks), the secondary
zone expires and no longer responds to queries.
Usually, all of the zone’s authoritative servers are listed in NS
records in the parent zone. These NS records constitute a delegation
of the zone from the parent. The authoritative servers are also listed
in the zone file itself, at the top level or apex of the zone.
Servers that are not in the parent’s NS delegation can be listed in the
zone’s top-level NS records, but servers that are not present at the
zone’s top level cannot be listed in the parent’s delegation.
A stealth server is a server that is authoritative for a zone but is
not listed in that zone’s NS records. Stealth servers can be used for
keeping a local copy of a zone, to speed up access to the zone’s records
or to make sure that the zone is available even if all the “official”
servers for the zone are inaccessible.
A configuration where the primary server itself is a stealth
server is often referred to as a “hidden primary” configuration. One use
for this configuration is when the primary is behind a firewall
and is therefore unable to communicate directly with the outside world.
The resolver libraries provided by most operating systems are stub
resolvers, meaning that they are not capable of performing the full DNS
resolution process by themselves by talking directly to the
authoritative servers. Instead, they rely on a local name server to
perform the resolution on their behalf. Such a server is called a
recursive name server; it performs recursive lookups for local
clients.
To improve performance, recursive servers cache the results of the
lookups they perform. Since the processes of recursion and caching are
intimately connected, the terms recursive server and caching server
are often used synonymously.
The length of time for which a record may be retained in the cache of a
caching name server is controlled by the Time-To-Live (TTL) field
associated with each resource record.
Even a caching name server does not necessarily perform the complete
recursive lookup itself. Instead, it can forward some or all of the
queries that it cannot satisfy from its cache to another caching name
server, commonly referred to as a forwarder.
Forwarders are typically used when an administrator does not wish for
all the servers at a given site to interact directly with the rest of
the Internet. For example, a common scenario is when multiple internal
DNS servers are behind an Internet firewall. Servers behind the firewall
forward their requests to the server with external access, which queries
Internet DNS servers on the internal servers’ behalf.
Another scenario (largely now superseded by Response Policy Zones) is to
send queries first to a custom server for RBL processing before
forwarding them to the wider Internet.
There may be one or more forwarders in a given setup. The order in which
the forwarders are listed in named.conf does not determine the
sequence in which they are queried; rather, named uses the response
times from previous queries to select the server that is likely to
respond the most quickly. A server that has not yet been queried is
given an initial small random response time to ensure that it is tried
at least once. Dynamic adjustment of the recorded response times ensures
that all forwarders are queried, even those with slower response times.
This permits changes in behavior based on server responsiveness.
The BIND name server can simultaneously act as a primary for some zones,
a secondary for other zones, and as a caching (recursive) server for a set
of local clients.
However, since the functions of authoritative name service and
caching/recursive name service are logically separate, it is often
advantageous to run them on separate server machines. A server that only
provides authoritative name service (an authoritative-only server) can
run with recursion disabled, improving reliability and security. A
server that is not authoritative for any zones and only provides
recursive service to local clients (a caching-only server) does not
need to be reachable from the Internet at large and can be placed inside
a firewall.
DNS hardware requirements have traditionally been quite modest. For many
installations, servers that have been retired from active duty
have performed admirably as DNS servers.
However, the DNSSEC features of BIND 9 may be quite CPU-intensive,
so organizations that make heavy use of these features may wish
to consider larger systems for these applications. BIND 9 is fully
multithreaded, allowing full utilization of multiprocessor systems for
installations that need it.
CPU requirements for BIND 9 range from i386-class machines, for serving
static zones without caching, to enterprise-class machines
to process many dynamic updates and DNSSEC-signed zones, serving
many thousands of queries per second.
Server memory must be sufficient to hold both the cache and the
zones loaded from disk. The max-cache-size option can
limit the amount of memory used by the cache, at the expense of reducing
cache hit rates and causing more DNS traffic. It is still good practice
to have enough memory to load all zone and cache data into memory;
unfortunately, the best way to determine this for a given installation
is to watch the name server in operation. After a few weeks, the server
process should reach a relatively stable size where entries are expiring
from the cache as fast as they are being inserted.
For name server-intensive environments, there are two
configurations that may be used. The first is one where clients and any
second-level internal name servers query the main name server, which has
enough memory to build a large cache; this approach minimizes the
bandwidth used by external name lookups. The second alternative is to
set up second-level internal name servers to make queries independently.
In this configuration, none of the individual machines need to have as
much memory or CPU power as in the first alternative, but this has the
disadvantage of making many more external queries, as none of the name
servers share their cached data.
In general, this version of BIND will build and run on any
POSIX-compliant system with a C11-compliant C compiler, BSD-style
sockets with RFC-compliant IPv6 support, POSIX-compliant threads, and
the required libraries.
The following C11 features are used in BIND 9:
Atomic operations support from the compiler is needed, either in the
form of builtin operations, C11 atomics, or the Interlocked
family of functions on Windows.
Thread Local Storage support from the compiler is needed, either in
the form of C11 _Thread_local/thread_local, the __thread
GCC extension, or the __declspec(thread) MSVC extension on
Windows.
ISC regularly tests BIND on many operating systems and architectures,
but lacks the resources to test all of them. Consequently, ISC is only
able to offer support on a “best effort” basis for some.
The following are platforms on which BIND is known to build and run. ISC
makes every effort to fix bugs on these platforms, but may be unable to
do so quickly due to lack of hardware, less familiarity on the part of
engineering staff, and other constraints. With the exception of Windows
Server 2016, none of these are tested regularly by ISC.
Windows Server 2012 R2, 2016 / x64
Windows 10 / x64
macOS 10.12+
Solaris 11
NetBSD
Other Linux distributions still supported by their vendors, such as:
These systems may not all have the required dependencies for building
BIND easily available, although it will be possible in many cases to
compile those directly from source. The community and interested parties
may wish to help with maintenance, and we welcome patch contributions,
although we cannot guarantee that we will accept them. All contributions
will be assessed against the risk of adverse effect on officially
supported platforms.
Platforms past or close to their respective EOL dates, such as:
Ubuntu 14.04, 16.04 (Ubuntu ESM releases are not supported)
To build BIND 9, the following packages must be installed:
libcrypto, libssl
libuv
perl
pkg-config / pkgconfig / pkgconf
BIND 9.16 requires libuv 1.0.0 or higher, using libuv >= 1.40.0
is recommended. Compiling or running with libuv 1.35.0 or 1.36.0 is
not supported, as this could lead to an assertion failure in the UDP
receive code. On older systems, an updated libuv package needs to be
installed from sources such as EPEL, PPA, or other native sources. The
other option is to build and install libuv from source.
OpenSSL 1.0.2e or newer is required. If the OpenSSL library is installed
in a nonstandard location, specify the prefix using
--with-openssl=<PREFIX> on the configure command line.
Portions of BIND that are written in Python, including
dnssec-keymgr, dnssec-coverage, dnssec-checkds, and some of
the system tests, require the argparse, ply and
distutils.core modules to be available. argparse is a standard
module as of Python 2.7 and Python 3.2. ply is available from
https://pypi.python.org/pypi/ply. distutils.core is required for
installation.
To see a full list of configuration options, run configure--help.
To build shared libraries, specify --with-libtool on the
configure command line.
To support the HTTP statistics channel, the server must be linked with
at least one of the following libraries: libxml2
(http://xmlsoft.org) or json-c (https://github.com/json-c/json-c).
If these are installed at a nonstandard location, then:
for libxml2, specify the prefix using --with-libxml2=/prefix,
for json-c, adjust PKG_CONFIG_PATH.
To support compression on the HTTP statistics channel, the server must
be linked against zlib (https://zlib.net/). If this is installed in
a nonstandard location, specify the prefix using
--with-zlib=/prefix.
To support storing configuration data for runtime-added zones in an LMDB
database, the server must be linked with liblmdb
(https://github.com/LMDB/lmdb). If this is installed in a nonstandard
location, specify the prefix using --with-lmdb=/prefix.
To support MaxMind GeoIP2 location-based ACLs, the server must be linked
with libmaxminddb (https://maxmind.github.io/libmaxminddb/). This is
turned on by default if the library is found; if the library is
installed in a nonstandard location, specify the prefix using
--with-maxminddb=/prefix. GeoIP2 support can be switched off with
--disable-geoip.
To support internationalized domain names in dig, libidn2
(https://www.gnu.org/software/libidn/#libidn2) must be installed. If the
library is installed in a nonstandard location, specify the prefix using
--with-libidn2=/prefix or adjust PKG_CONFIG_PATH.
For line editing in nsupdate and nslookup, either the
readline (https://tiswww.case.edu/php/chet/readline/rltop.html) or
the libedit library (https://www.thrysoee.dk/editline/) must be
installed. If these are installed at a nonstandard location, adjust
PKG_CONFIG_PATH. readline is used by default, and libedit
can be explicitly requested using --with-readline=libedit.
Certain compiled-in constants and default settings can be decreased to
values better suited to small machines, e.g. OpenWRT boxes, by
specifying --with-tuning=small on the configure command line.
This decreases memory usage by using smaller structures, but degrades
performance.
On Linux, process capabilities are managed in user space using the
libcap library
(https://git.kernel.org/pub/scm/libs/libcap/libcap.git/), which can be
installed on most Linux systems via the libcap-dev or
libcap-devel package. Process capability support can also be
disabled by configuring with --disable-linux-caps.
On some platforms it is necessary to explicitly request large file
support to handle files bigger than 2GB. This can be done by using
--enable-largefile on the configure command line.
Support for the “fixed” RRset-order option can be enabled or disabled by
specifying --enable-fixed-rrset or --disable-fixed-rrset on the
configure command line. By default, fixed RRset-order is disabled to
reduce memory footprint.
The --enable-querytrace option causes named to log every step
while processing every query. This option should only be enabled when
debugging because is has a significant negative impact on query
performance.
makeinstall installs named and the various BIND 9 libraries. By
default, installation is into /usr/local, but this can be changed with
the --prefix option when running configure.
The option --sysconfdir can be specified to set the directory where
configuration files such as named.conf go by default;
--localstatedir can be used to set the default parent directory of
run/named.pid. --sysconfdir defaults to $prefix/etc and
--localstatedir defaults to $prefix/var.
Building on macOS assumes that the “Command Tools for Xcode” are
installed. These can be downloaded from
https://developer.apple.com/download/more/ or, if Xcode is already
installed, simply run xcode-select--install. (Note that an Apple ID
may be required to access the download page.)
In this chapter we provide some suggested configurations, along with
guidelines for their use. We suggest reasonable values for certain
option settings.
The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation. All queries
from outside clients are refused using the allow-query option.
The same effect can be achieved using suitable firewall
rules.
This sample configuration is for an authoritative-only server that is
the primary server for example.com and a secondary server for the subdomain
eng.example.com.
A primitive form of load balancing can be achieved in the DNS by using
multiple records (such as multiple A records) for one name.
For example, assuming three HTTP servers with network addresses of
10.0.0.1, 10.0.0.2, and 10.0.0.3, a set of records such as the following
means that clients will connect to each machine one-third of the time:
Name
TTL
CLASS
TYPE
Resource Record (RR) Data
www
600
IN
A
10.0.0.1
600
IN
A
10.0.0.2
600
IN
A
10.0.0.3
When a resolver queries for these records, BIND rotates them and
responds to the query with the records in a different order. In the
example above, clients randomly receive records in the order 1, 2,
3; 2, 3, 1; and 3, 1, 2. Most clients use the first record returned
and discard the rest.
For more detail on ordering responses, check the rrset-order
sub-statement in the options statement; see RRset Ordering.
This section describes several indispensable diagnostic, administrative,
and monitoring tools available to the system administrator for
controlling and debugging the name server daemon.
The dig, host, and nslookup programs are all command-line
tools for manually querying name servers. They differ in style and
output format.
dig
dig is the most versatile and complete of these lookup tools. It
has two modes: simple interactive mode for a single query, and batch
mode, which executes a query for each in a list of several query
lines. All query options are accessible from the command line.
For more information and a list of available commands and options,
see dig - DNS lookup utility.
host
The host utility emphasizes simplicity and ease of use. By
default, it converts between host names and Internet addresses, but
its functionality can be extended with the use of options.
nslookup has two modes: interactive and non-interactive.
Interactive mode allows the user to query name servers for
information about various hosts and domains, or to print a list of
hosts in a domain. Non-interactive mode is used to print just the
name and requested information for a host or domain.
Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of nslookup. Use dig
instead.
rndc requires a configuration file, since all communication with
the server is authenticated with digital signatures that rely on a
shared secret, and there is no way to provide that secret other than
with a configuration file. The default location for the rndc
configuration file is /etc/rndc.conf, but an alternate location
can be specified with the -c option. If the configuration file is
not found, rndc also looks in /etc/rndc.key (or whatever
sysconfdir was defined when the BIND build was configured). The
rndc.key file is generated by running rndc-confgen-a as
described in controls Statement Definition and Usage.
The format of the configuration file is similar to that of
named.conf, but is limited to only four statements: the options,
key, server, and include statements. These statements are
what associate the secret keys to the servers with which they are
meant to be shared. The order of statements is not significant.
The options statement has three clauses: default-server,
default-key, and default-port. default-server takes a
host name or address argument and represents the server that is
contacted if no -s option is provided on the command line.
default-key takes the name of a key as its argument, as defined
by a key statement. default-port specifies the port to which
rndc should connect if no port is given on the command line or in
a server statement.
The key statement defines a key to be used by rndc when
authenticating with named. Its syntax is identical to the key
statement in named.conf. The keyword key is followed by a key
name, which must be a valid domain name, though it need not actually
be hierarchical; thus, a string like rndc_key is a valid name.
The key statement has two clauses: algorithm and secret.
While the configuration parser accepts any string as the argument
to algorithm, currently only the strings hmac-md5,
hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, and hmac-sha512 have any meaning. The secret
is a Base64-encoded string as specified in RFC 3548.
The server statement associates a key defined using the key
statement with a server. The keyword server is followed by a host
name or address. The server statement has two clauses: key
and port. The key clause specifies the name of the key to be
used when communicating with this server, and the port clause can
be used to specify the port rndc should connect to on the server.
A sample minimal configuration file is as follows:
This file, if installed as /etc/rndc.conf, allows the
command:
$rndcreload
to connect to 127.0.0.1 port 953 and causes the name server to reload,
if a name server on the local machine is running with the following
controls statements:
and it has an identical key statement for rndc_key.
Running the rndc-confgen program conveniently creates an
rndc.conf file, and also displays the corresponding
controls statement needed to add to named.conf.
Alternatively, it is possible to run rndc-confgen-a to set up an
rndc.key file and not modify named.conf at all.
Certain Unix signals cause the name server to take specific actions, as
described in the following table. These signals can be sent using the
kill command.
SIGHUP
Causes the server to read named.conf and reload
the database.
Plugins are a mechanism to extend the functionality of named using
dynamically loadable libraries. By using plugins, core server
functionality can be kept simple for the majority of users; more complex
code implementing optional features need only be installed by users that
need those features.
The plugin interface is a work in progress, and is expected to evolve as
more plugins are added. Currently, only “query plugins” are supported;
these modify the name server query logic. Other plugin types may be
added in the future.
The only plugin currently included in BIND is filter-aaaa.so, which
replaces the filter-aaaa feature that previously existed natively as
part of named. The code for this feature has been removed from
named and can no longer be configured using standard named.conf
syntax, but linking in the filter-aaaa.so plugin provides identical
functionality.
plugin_register
to allocate memory, configure a plugin instance, and attach to hook
points within
named
,
plugin_destroy
to tear down the plugin instance and free memory,
plugin_version
to check that the plugin is compatible with the current version of
the plugin API,
plugin_check
to test syntactic correctness of the plugin parameters.
At various locations within the named source code, there are “hook
points” at which a plugin may register itself. When a hook point is
reached while named is running, it is checked to see whether any
plugins have registered themselves there; if so, the associated “hook
action” - a function within the plugin library - is called. Hook
actions may examine the runtime state and make changes: for example,
modifying the answers to be sent back to a client or forcing a query to
be aborted. More details can be found in the file
lib/ns/include/ns/hooks.h.
An IPv6 address, such as 2001:db8::1234. IPv6-scoped addresses that have ambiguity on their scope zones must be disambiguated by an appropriate zone ID with the percent character (%) as a delimiter. It is strongly recommended to use string zone names rather than numeric identifiers, to be robust against system configuration changes. However, since there is no standard mapping for such names and identifier values, only interface names as link identifiers are supported, assuming one-to-one mapping between interfaces and links. For example, a link-local address fe80::1 on the link attached to the interface ne0 can be specified as fe80::1%ne0. Note that on most systems link-local addresses always have ambiguity and need to be disambiguated.
A number between 0 and 63, used to select a differentiated services code point (DSCP) value for use with outgoing traffic on operating systems that support DSCP.
An IP port number. The number is limited to 0 through 65535, with values below 1024 typically restricted to use by processes running as root. In some cases, an asterisk (*) character can be used as a placeholder to select a random high-numbered port.
An IP network specified as an ip_addr, followed by a slash (/) and then the number of bits in the netmask. Trailing zeros in an``ip_addr`` may be omitted. For example, 127/8 is the network 127.0.0.0``withnetmask``255.0.0.0 and 1.2.3.0/28 is network 1.2.3.0 with netmask 255.255.255.240.
When specifying a prefix involving a IPv6-scoped address, the scope may be omitted. In that case, the prefix matches packets from any scope.
A non-negative 32-bit integer (i.e., a number between 0 and 4294967295, inclusive). Its acceptable value might be further limited by the context in which it is used.
A non-negative real number that can be specified to the nearest one-hundredth. Up to five digits can be specified before a decimal point, and up to two digits after, so the maximum value is 99999.99. Acceptable values might be further limited by the contexts in which they are used.
A list of an ip_port or a port range. A port range is specified in the form of range followed by two ip_port``s,``port_low and port_high, which represents port numbers from port_low through port_high, inclusive. port_low must not be larger than port_high. For example, range102465535 represents ports from 1024 through 65535. In either case an asterisk (*) character is not allowed as a valid ip_port.
A 64-bit unsigned integer, or the keywords unlimited or default. Integers may take values 0 <= value <= 18446744073709551615, though certain parameters (such as max-journal-size) may use a more limited range within these extremes. In most cases, setting a value to 0 does not literally mean zero; it means “undefined” or “as big as possible,” depending on the context. See the explanations of particular parameters that use size_spec for details on how they interpret its use. Numeric values can optionally be followed by a scaling factor: K or k for kilobytes, M or m for megabytes, and G or g for gigabytes, which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.
unlimited generally means “as big as possible,” and is usually the best way to safely set a very large number.
default uses the limit that was in force when the server was started.
A size_spec or integer value followed by % to represent percent. The behavior is exactly the same as size_spec, but size_or_percent also allows specifying a positive integer value followed by the % sign to represent percent.
One of yes, no, notify, notify-passive, refresh, or passive. When used in a zone, notify-passive, refresh, and passive are restricted to secondary and stub zones.
Address match lists are primarily used to determine access control for
various server operations. They are also used in the listen-on and
sortlist statements. The elements which constitute an address match
list can be any of the following:
an IP address (IPv4 or IPv6)
an IP prefix (in / notation)
a key ID, as defined by the key statement
the name of an address match list defined with the acl statement
a nested address match list enclosed in braces
Elements can be negated with a leading exclamation mark (!), and the
match list names “any”, “none”, “localhost”, and “localnets” are
predefined. More information on those names can be found in the
description of the acl statement.
The addition of the key clause made the name of this syntactic element
something of a misnomer, since security keys can be used to validate
access without regard to a host or network address. Nonetheless, the
term “address match list” is still used throughout the documentation.
When a given IP address or prefix is compared to an address match list,
the comparison takes place in approximately O(1) time. However, key
comparisons require that the list of keys be traversed until a matching
key is found, and therefore may be somewhat slower.
The interpretation of a match depends on whether the list is being used
for access control, defining listen-on ports, or in a sortlist,
and whether the element was negated.
When used as an access control list, a non-negated match allows access
and a negated match denies access. If there is no match, access is
denied. The clauses allow-notify, allow-recursion,
allow-recursion-on, allow-query, allow-query-on,
allow-query-cache, allow-query-cache-on, allow-transfer,
allow-update, allow-update-forwarding, blackhole, and
keep-response-order all use address match lists. Similarly, the
listen-on option causes the server to refuse queries on any of
the machine’s addresses which do not match the list.
Order of insertion is significant. If more than one element in an ACL is
found to match a given IP address or prefix, preference is given to
the one that came first in the ACL definition. Because of this
first-match behavior, an element that defines a subset of another
element in the list should come before the broader element, regardless
of whether either is negated. For example, in 1.2.3/24;!1.2.3.13;
the 1.2.3.13 element is completely useless because the algorithm
matches any lookup for 1.2.3.13 to the 1.2.3/24 element. Using
!1.2.3.13;1.2.3/24 fixes that problem by blocking 1.2.3.13
via the negation, but all other 1.2.3.* hosts pass through.
The BIND 9 comment syntax allows comments to appear anywhere that
whitespace may appear in a BIND configuration file. To appeal to
programmers of all kinds, they can be written in the C, C++, or
shell/perl style.
Comments may appear anywhere that whitespace may appear in a BIND
configuration file.
C-style comments start with the two characters /* (slash, star) and end
with */ (star, slash). Because they are completely delimited with these
characters, they can be used to comment only a portion of a line or to
span multiple lines.
C-style comments cannot be nested. For example, the following is not
valid because the entire comment ends with the first */:
C++-style comments start with the two characters // (slash, slash) and
continue to the end of the physical line. They cannot be continued
across multiple physical lines; to have one logical comment span
multiple lines, each line must use the // pair. For example:
Shell-style (or perl-style) comments start with the
character # (number sign) and continue to the end of the physical
line, as in C++ comments. For example:
# This is the start of a comment. The next line# is a new comment, even though it is logically# part of the previous comment.
Warning
The semicolon (;) character cannot start a comment, unlike
in a zone file. The semicolon indicates the end of a
configuration statement.
A BIND 9 configuration consists of statements and comments. Statements
end with a semicolon; statements and comments are the only elements that
can appear without enclosing braces. Many statements contain a block of
sub-statements, which are also terminated with a semicolon.
The following statements are supported:
acl
Defines a named IP address matching list, for access control and other uses.
controls
Declares control channels to be used by the rndc utility.
dnssec-policy
Describes a DNSSEC key and signing policy for zones. See dnssec-policy Grammar for details.
include
Includes a file.
key
Specifies key information for use in authentication and authorization using TSIG.
logging
Specifies what information the server logs and where the log messages are sent.
masters
Synonym for primaries.
options
Controls global server configuration options and sets defaults for other statements.
parental-agents
Defines a named list of servers for inclusion in primary and secondary zones’ parental-agents lists.
primaries
Defines a named list of servers for inclusion in stub and secondary zones’ primaries or also-notify lists. (Note: this is a synonym for the original keyword masters, which can still be used, but is no longer the preferred terminology.)
server
Sets certain configuration options on a per-server basis.
statistics-channels
Declares communication channels to get access to named statistics.
trust-anchors
Defines DNSSEC trust anchors: if used with the initial-key or initial-ds keyword, trust anchors are kept up-to-date using RFC 5011 trust anchor maintenance; if used with static-key or static-ds, keys are permanent.
managed-keys
Is identical to trust-anchors; this option is deprecated in favor of trust-anchors with the initial-key keyword, and may be removed in a future release.
trusted-keys
Defines permanent trusted DNSSEC keys; this option is deprecated in favor of trust-anchors with the static-key keyword, and may be removed in a future release.
view
Defines a view.
zone
Defines a zone.
The logging and options statements may only occur once per
configuration.
The acl statement assigns a symbolic name to an address match list.
It gets its name from one of the primary uses of address match lists: Access
Control Lists (ACLs).
The following ACLs are built-in:
any
Matches all hosts.
none
Matches no hosts.
localhost
Matches the IPv4 and IPv6 addresses of all network interfaces on the system. When addresses are added or removed, the localhost ACL element is updated to reflect the changes.
localnets
Matches any host on an IPv4 or IPv6 network for which the system has an interface. When addresses are added or removed, the localnets ACL element is updated to reflect the changes. Some systems do not provide a way to determine the prefix lengths of local IPv6 addresses; in such cases, localnets only matches the local IPv6 addresses, just like localhost.
The controls statement declares control channels to be used by
system administrators to manage the operation of the name server. These
control channels are used by the rndc utility to send commands to
and retrieve non-DNS results from a name server.
An inet control channel is a TCP socket listening at the specified
ip_port on the specified ip_addr, which can be an IPv4 or IPv6
address. An ip_addr of * (asterisk) is interpreted as the IPv4
wildcard address; connections are accepted on any of the system’s
IPv4 addresses. To listen on the IPv6 wildcard address, use an
ip_addr of ::. If rndc is only used on the local host,
using the loopback address (127.0.0.1 or ::1) is recommended for
maximum security.
If no port is specified, port 953 is used. The asterisk * cannot
be used for ip_port.
The ability to issue commands over the control channel is restricted by
the allow and keys clauses. Connections to the control channel
are permitted based on the address_match_list. This is for simple IP
address-based filtering only; any key_id elements of the
address_match_list are ignored.
A unix control channel is a Unix domain socket listening at the
specified path in the file system. Access to the socket is specified by
the perm, owner, and group clauses. Note that on some platforms
(SunOS and Solaris), the permissions (perm) are applied to the parent
directory as the permissions on the socket itself are ignored.
The primary authorization mechanism of the command channel is the
key_list, which contains a list of key_id``s.Each``key_id in
the key_list is authorized to execute commands over the control
channel. See Administrative Tools for information about
configuring keys in rndc.
If the read-only clause is enabled, the control channel is limited
to the following set of read-only commands: nta-dump, null,
status, showzone, testgen, and zonestatus. By default,
read-only is not enabled and the control channel allows read-write
access.
If no controls statement is present, named sets up a default
control channel listening on the loopback address 127.0.0.1 and its IPv6
counterpart, ::1. In this case, and also when the controls statement
is present but does not have a keys clause, named attempts
to load the command channel key from the file rndc.key in /etc
(or whatever sysconfdir was specified when BIND was built). To
create an rndc.key file, run rndc-confgen-a.
To disable the command channel, use an empty controls statement:
controls{};.
The include statement inserts the specified file (or files if a valid glob
expression is detected) at the point where the include statement is
encountered. The include statement facilitates the administration of
configuration files by permitting the reading or writing of some things but not
others. For example, the statement could include private keys that are readable
only by the name server.
The key statement can occur at the top level of the configuration
file or inside a view statement. Keys defined in top-level key
statements can be used in all views. Keys intended for use in a
controls statement (see controls Statement Definition and Usage)
must be defined at the top level.
The key_id, also known as the key name, is a domain name that uniquely
identifies the key. It can be used in a server statement to cause
requests sent to that server to be signed with this key, or in address
match lists to verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
The algorithm_id is a string that specifies a security/authentication
algorithm. The named server supports hmac-md5, hmac-sha1,
hmac-sha224, hmac-sha256, hmac-sha384, and hmac-sha512
TSIG authentication. Truncated hashes are supported by appending the
minimum number of required bits preceded by a dash, e.g.,
hmac-sha1-80. The secret_string is the secret to be used by the
algorithm, and is treated as a Base64-encoded string.
The logging statement configures a wide variety of logging options
for the name server. Its channel phrase associates output methods,
format options, and severity levels with a name that can then be used
with the category phrase to select how various classes of messages
are logged.
Only one logging statement is used to define as many channels and
categories as desired. If there is no logging statement, the
logging configuration is:
The logging configuration is only established when the entire
configuration file has been parsed. When the server starts up, all
logging messages regarding syntax errors in the configuration file go to
the default channels, or to standard error if the -g option was
specified.
All log output goes to one or more channels; there is no limit to
the number of channels that can be created.
Every channel definition must include a destination clause that says
whether messages selected for the channel go to a file, go to a particular
syslog facility, go to the standard error stream, or are discarded. The definition can
optionally also limit the message severity level that is accepted
by the channel (the default is info), and whether to include a
named-generated time stamp, the category name, and/or the severity level
(the default is not to include any).
The null destination clause causes all messages sent to the channel
to be discarded; in that case, other options for the channel are
meaningless.
The file destination clause directs the channel to a disk file. It
can include additional arguments to specify how large the file is
allowed to become before it is rolled to a backup file (size), how
many backup versions of the file are saved each time this happens
(versions), and the format to use for naming backup versions
(suffix).
The size option is used to limit log file growth. If the file ever
exceeds the specified size, then named stops writing to the file
unless it has a versions option associated with it. If backup
versions are kept, the files are rolled as described below. If there is
no versions option, no more data is written to the log until
some out-of-band mechanism removes or truncates the log to less than the
maximum size. The default behavior is not to limit the size of the file.
File rolling only occurs when the file exceeds the size specified with
the size option. No backup versions are kept by default; any
existing log file is simply appended. The versions option specifies
how many backup versions of the file should be kept. If set to
unlimited, there is no limit.
The suffix option can be set to either increment or
timestamp. If set to timestamp, then when a log file is rolled,
it is saved with the current timestamp as a file suffix. If set to
increment, then backup files are saved with incrementing numbers as
suffixes; older files are renamed when rolling. For example, if
versions is set to 3 and suffix to increment, then when
filename.log reaches the size specified by size,
filename.log.1 is renamed to filename.log.2, filename.log.0
is renamed to filename.log.1, and filename.log is renamed to
filename.log.0, whereupon a new filename.log is opened.
Here is an example using the size, versions, and suffix options:
The syslog destination clause directs the channel to the system log.
Its argument is a syslog facility as described in the syslog man
page. Known facilities are kern, user, mail, daemon,
auth, syslog, lpr, news, uucp, cron,
authpriv, ftp, local0, local1, local2, local3,
local4, local5, local6, and local7; however, not all
facilities are supported on all operating systems. How syslog
handles messages sent to this facility is described in the
syslog.conf man page. On a system which uses a very old
version of syslog, which only uses two arguments to the openlog()
function, this clause is silently ignored.
On Windows machines, syslog messages are directed to the EventViewer.
The severity clause works like syslog’s “priorities,” except
that they can also be used when writing straight to a file rather
than using syslog. Messages which are not at least of the severity
level given are not selected for the channel; messages of higher
severity levels are accepted.
When using syslog, the syslog.conf priorities
also determine what eventually passes through. For example, defining a
channel facility and severity as daemon and debug, but only
logging daemon.warning via syslog.conf, causes messages of
severity info and notice to be dropped. If the situation were
reversed, with named writing messages of only warning or higher,
then syslogd would print all messages it received from the channel.
The stderr destination clause directs the channel to the server’s
standard error stream. This is intended for use when the server is
running as a foreground process, as when debugging a
configuration, for example.
The server can supply extensive debugging information when it is in
debugging mode. If the server’s global debug level is greater than zero,
debugging mode is active. The global debug level is set either
by starting the named server with the -d flag followed by a
positive integer, or by running rndctrace. The global debug level
can be set to zero, and debugging mode turned off, by running rndcnotrace. All debugging messages in the server have a debug level;
higher debug levels give more detailed output. Channels that specify a
specific debug severity, for example:
get debugging output of level 3 or less any time the server is in
debugging mode, regardless of the global debugging level. Channels with
dynamic severity use the server’s global debug level to determine
what messages to print.
print-time can be set to yes, no, or a time format
specifier, which may be one of local, iso8601, or
iso8601-utc. If set to no, the date and time are not
logged. If set to yes or local, the date and time are logged in
a human-readable format, using the local time zone. If set to
iso8601, the local time is logged in ISO 8601 format. If set to
iso8601-utc, the date and time are logged in ISO 8601 format,
with time zone set to UTC. The default is no.
print-time may be specified for a syslog channel, but it is
usually pointless since syslog also logs the date and time.
If print-category is requested, then the category of the message
is logged as well. Finally, if print-severity is on, then the
severity level of the message is logged. The print- options may
be used in any combination, and are always printed in the following
order: time, category, severity. Here is an example where all three
print- options are on:
28-Feb-200015:05:32.863general:notice:running
If buffered has been turned on, the output to files is not
flushed after each log entry. By default all log messages are flushed.
There are four predefined channels that are used for named’s default
logging, as follows. If named is started with the -L option, then a fifth
channel, default_logfile, is added. How they are used is described in
The category Phrase.
channeldefault_syslog{//sendtosyslog's daemon facilitysyslogdaemon;//onlysendpriorityinfoandhigherseverityinfo;};channeldefault_debug{//writetonamed.runintheworkingdirectory//Note:stderrisusedinsteadof"named.run"if//theserverisstartedwiththe'-g'option.file"named.run";//logattheserver's current debug levelseveritydynamic;};channeldefault_stderr{//writestostderrstderr;//onlysendpriorityinfoandhigherseverityinfo;};channelnull{//tossanythingsenttothischannelnull;};channeldefault_logfile{//thischannelisonlypresentifnamedis//startedwiththe-Loption,whoseargument//providesthefilenamefile"...";//logattheserver's current debug levelseveritydynamic;};
The default_debug channel has the special property that it only
produces output when the server’s debug level is non-zero. It normally
writes to a file called named.run in the server’s working directory.
For security reasons, when the -u command-line option is used, the
named.run file is created only after named has changed to the
new UID, and any debug output generated while named is starting -
and still running as root - is discarded. To capture this
output, run the server with the -L option to specify a
default logfile, or the -g option to log to standard error which can
be redirected to a file.
Once a channel is defined, it cannot be redefined. The
built-in channels cannot be altered directly, but the default logging
can be modified by pointing categories at defined channels.
There are many categories, so desired logs can be sent anywhere
while unwanted logs are ignored. If
a list of channels is not specified for a category, log messages in that
category are sent to the default category instead. If no
default category is specified, the following “default default” is used:
categorydefault{default_syslog;default_debug;};
If named is started with the -L option, the default category
is:
categorydefault{default_logfile;default_debug;};
As an example, let’s say a user wants to log security events to a file, but
also wants to keep the default logging behavior. They would specify the
following:
To discard all messages in a category, specify the null channel:
categoryxfer-out{null;};categorynotify{null;};
The following are the available categories and brief descriptions of the
types of log information they contain. More categories may be added in
future BIND releases.
client
Processing of client requests.
cname
Name servers that are skipped for being a CNAME rather than A/AAAA records.
config
Configuration file parsing and processing.
database
Messages relating to the databases used internally by the name server to store zone and cache data.
default
Logging options for those categories where no specific configuration has been defined.
delegation-only
Queries that have been forced to NXDOMAIN as the result of a delegation-only zone or a delegation-only in a forward, hint, or stub zone declaration.
dispatch
Dispatching of incoming packets to the server modules where they are to be processed.
dnssec
DNSSEC and TSIG protocol processing.
dnstap
The “dnstap” DNS traffic capture system.
edns-disabled
Log queries that have been forced to use plain DNS due to timeouts. This is often due to the remote servers not being RFC 1034-compliant (not always returning FORMERR or similar to EDNS queries and other extensions to the DNS when they are not understood). In other words, this is targeted at servers that fail to respond to DNS queries that they don’t understand.
Note: the log message can also be due to packet loss. Before reporting servers for non-RFC 1034 compliance they should be re-tested to determine the nature of the non-compliance. This testing should prevent or reduce the number of false-positive reports.
Note: eventually named will have to stop treating such timeouts as due to RFC 1034 non-compliance and start treating it as plain packet loss. Falsely classifying packet loss as due to RFC 1034 non-compliance impacts DNSSEC validation, which requires EDNS for the DNSSEC records to be returned.
general
A catch-all for many things that still are not classified into categories.
lame-servers
Misconfigurations in remote servers, discovered by BIND 9 when trying to query those servers during resolution.
network
Network operations.
notify
The NOTIFY protocol.
nsid
NSID options received from upstream servers.
queries
A location where queries should be logged.
At startup, specifying the category queries also enables query logging unless the querylog option has been specified.
The query log entry first reports a client object identifier in @0x<hexadecimal-number> format. Next, it reports the client’s IP address and port number, and the query name, class, and type. Next, it reports whether the Recursion Desired flag was set (+ if set, - if not set), whether the query was signed (S), whether EDNS was in use along with the EDNS version number (E(#)), whether TCP was used (T), whether DO (DNSSEC Ok) was set (D), whether CD (Checking Disabled) was set (C), whether a valid DNS Server COOKIE was received (V), and whether a DNS COOKIE option without a valid Server COOKIE was present (K). After this, the destination address the query was sent to is reported. Finally, if any CLIENT-SUBNET option was present in the client query, it is included in square brackets in the format [ECS address/source/scope].
The first part of this log message, showing the client address/port number and query name, is repeated in all subsequent log messages related to the same query.
query-errors
Information about queries that resulted in some failure.
rate-limit
Start, periodic, and final notices of the rate limiting of a stream of responses that are logged at info severity in this category. These messages include a hash value of the domain name of the response and the name itself, except when there is insufficient memory to record the name for the final notice. The final notice is normally delayed until about one minute after rate limiting stops. A lack of memory can hurry the final notice, which is indicated by an initial asterisk (*). Various internal events are logged at debug level 1 and higher.
Rate limiting of individual requests is logged in the query-errors category.
resolver
DNS resolution, such as the recursive lookups performed on behalf of clients by a caching name server.
rpz
Information about errors in response policy zone files, rewritten responses, and, at the highest debug levels, mere rewriting attempts.
security
Approval and denial of requests.
serve-stale
Indication of whether a stale answer is used following a resolver failure.
spill
Queries that have been terminated, either by dropping or responding with SERVFAIL, as a result of a fetchlimit quota being exceeded.
trust-anchor-telemetry
Trust-anchor-telemetry requests received by named.
unmatched
Messages that named was unable to determine the class of, or for which there was no matching view. A one-line summary is also logged to the client category. This category is best sent to a file or stderr; by default it is sent to the null channel.
update
Dynamic updates.
update-security
Approval and denial of update requests.
xfer-in
Zone transfers the server is receiving.
xfer-out
Zone transfers the server is sending.
zoneload
Loading of zones and creation of automatic empty zones.
The query-errors category is used to indicate why and how specific queries
resulted in responses which indicate an error. Normally, these messages are
logged at debug logging levels; note, however, that if query logging is
active, some are logged at info. The logging levels are described below:
At debug level 1 or higher - or at info when query logging is
active - each response with the rcode of SERVFAIL is logged as follows:
This means an error resulting in SERVFAIL was detected at line 3880 of source
file query.c. Log messages of this level are particularly helpful in identifying
the cause of SERVFAIL for an authoritative server.
At debug level 2 or higher, detailed context information about recursive
resolutions that resulted in SERVFAIL is logged. The log message looks
like this:
The first part before the colon shows that a recursive resolution for
AAAA records of www.example.com completed in 10.000183 seconds, and the
final result that led to the SERVFAIL was determined at line 2970 of
source file resolver.c.
The next part shows the detected final result and the latest result of
DNSSEC validation. The latter is always “success” when no validation attempt
was made. In this example, this query probably resulted in SERVFAIL because all
name servers are down or unreachable, leading to a timeout in 10 seconds.
DNSSEC validation was probably not attempted.
The last part, enclosed in square brackets, shows statistics collected for this
particular resolution attempt. The domain field shows the deepest zone that
the resolver reached; it is the zone where the error was finally detected. The
meaning of the other fields is summarized in the following list.
referral
The number of referrals the resolver received throughout the resolution process. In the above example.com there are two.
restart
The number of cycles that the resolver tried remote servers at the domain zone. In each cycle, the resolver sends one query (possibly resending it, depending on the response) to each known name server of the domain zone.
qrysent
The number of queries the resolver sent at the domain zone.
timeout
The number of timeouts the resolver received since the last response.
lame
The number of lame servers the resolver detected at the domain zone. A server is detected to be lame either by an invalid response or as a result of lookup in BIND 9’s address database (ADB), where lame servers are cached.
quota
The number of times the resolver was unable to send a query because it had exceeded the permissible fetch quota for a server.
neterr
The number of erroneous results that the resolver encountered in sending queries at the domain zone. One common case is when the remote server is unreachable and the resolver receives an “ICMP unreachable” error message.
badresp
The number of unexpected responses (other than lame) to queries sent by the resolver at the domain zone.
adberr
Failures in finding remote server addresses of the``domain`` zone in the ADB. One common case of this is that the remote server’s name does not have any address records.
findfail
Failures to resolve remote server addresses. This is a total number of failures throughout the resolution process.
valfail
Failures of DNSSEC validation. Validation failures are counted throughout the resolution process (not limited to the domain zone), but should only happen in domain.
At debug level 3 or higher, the same messages as those at
debug level 1 are logged for errors other than
SERVFAIL. Note that negative responses such as NXDOMAIN are not errors, and are
not logged at this debug level.
At debug level 4 or higher, the detailed context information logged at
debug level 2 is logged for errors other than SERVFAIL and for negative
responses such as NXDOMAIN.
parental-agents lists allow for a common set of parental agents to be easily
used by multiple primary and secondary zones in their parental-agents lists.
A parental agent is the entity that the zone has a relationship with to
change its delegation information (defined in RFC 7344).
primaries lists allow for a common set of primary servers to be easily
used by multiple stub and secondary zones in their primaries or
also-notify lists. (Note: primaries is a synonym for the original
keyword masters, which can still be used, but is no longer the
preferred terminology.)
The options statement sets up global options to be used by BIND.
This statement may appear only once in a configuration file. If there is
no options statement, an options block with each option set to its
default is used.
attach-cache
This option allows multiple views to share a single cache database. Each view has
its own cache database by default, but if multiple views have the
same operational policy for name resolution and caching, those views
can share a single cache to save memory, and possibly improve
resolution efficiency, by using this option.
The attach-cache option may also be specified in view
statements, in which case it overrides the global attach-cache
option.
The cache_name specifies the cache to be shared. When the named
server configures views which are supposed to share a cache, it
creates a cache with the specified name for the first view of these
sharing views. The rest of the views simply refer to the
already-created cache.
One common configuration to share a cache is to allow all views
to share a single cache. This can be done by specifying
attach-cache as a global option with an arbitrary name.
Another possible operation is to allow a subset of all views to share
a cache while the others retain their own caches. For example, if
there are three views A, B, and C, and only A and B should share a
cache, specify the attach-cache option as a view of A (or B)’s
option, referring to the other view name:
Views that share a cache must have the same policy on configurable
parameters that may affect caching. The current implementation
requires the following configurable options be consistent among these
views: check-names, dnssec-accept-expired,
dnssec-validation, max-cache-ttl, max-ncache-ttl,
max-stale-ttl, max-cache-size, min-cache-ttl,
min-ncache-ttl, and zero-no-soa-ttl.
Note that there may be other parameters that may cause confusion if
they are inconsistent for different views that share a single cache.
For example, if these views define different sets of forwarders that
can return different answers for the same question, sharing the
answer does not make sense or could even be harmful. It is the
administrator’s responsibility to ensure that configuration differences in
different views do not cause disruption with a shared cache.
directory
This sets the working directory of the server. Any non-absolute pathnames in
the configuration file are taken as relative to this directory.
The default location for most server output files (e.g.,
named.run) is this directory. If a directory is not specified,
the working directory defaults to ".", the directory from
which the server was started. The directory specified should be an
absolute path, and must be writable by the effective user ID of the
named process.
The option takes effect only at the time that the configuration
option is parsed; if other files are being included before or after specifying the
new directory, the directory option must be listed
before any other directive (like include) that can work with relative
files. The safest way to include files is to use absolute file names.
dnstap
dnstap is a fast, flexible method for capturing and logging DNS
traffic. Developed by Robert Edmonds at Farsight Security, Inc., and
supported by multiple DNS implementations, dnstap uses
libfstrm (a lightweight high-speed framing library; see
https://github.com/farsightsec/fstrm) to send event payloads which
are encoded using Protocol Buffers (libprotobuf-c, a mechanism
for serializing structured data developed by Google, Inc.; see
https://developers.google.com/protocol-buffers/).
To enable dnstap at compile time, the fstrm and
protobuf-c libraries must be available, and BIND must be
configured with --enable-dnstap.
The dnstap option is a bracketed list of message types to be
logged. These may be set differently for each view. Supported types
are client, auth, resolver, forwarder, and
update. Specifying type all causes all dnstap
messages to be logged, regardless of type.
Each type may take an additional argument to indicate whether to log
query messages or response messages; if not specified, both
queries and responses are logged.
Example: To log all authoritative queries and responses, recursive
client responses, and upstream queries sent by the resolver, use:
The fstrm library has a number of tunables that are exposed in
named.conf, and can be modified if necessary to improve
performance or prevent loss of data. These are:
fstrm-set-buffer-hint: The threshold number of bytes to
accumulate in the output buffer before forcing a buffer flush. The
minimum is 1024, the maximum is 65536, and the default is 8192.
fstrm-set-flush-timeout: The number of seconds to allow
unflushed data to remain in the output buffer. The minimum is 1
second, the maximum is 600 seconds (10 minutes), and the default
is 1 second.
fstrm-set-output-notify-threshold: The number of outstanding
queue entries to allow on an input queue before waking the I/O
thread. The minimum is 1 and the default is 32.
fstrm-set-output-queue-model: The queuing semantics
to use for queue objects. The default is mpsc (multiple
producer, single consumer); the other option is spsc (single
producer, single consumer).
fstrm-set-input-queue-size: The number of queue entries to
allocate for each input queue. This value must be a power of 2.
The minimum is 2, the maximum is 16384, and the default is 512.
fstrm-set-output-queue-size: The number of queue entries to
allocate for each output queue. The minimum is 2, the maximum is
system-dependent and based on IOV_MAX, and the default is 64.
fstrm-set-reopen-interval: The number of seconds to wait
between attempts to reopen a closed output stream. The minimum is
1 second, the maximum is 600 seconds (10 minutes), and the default
is 5 seconds. For convenience, TTL-style time-unit suffixes may be
used to specify the value.
Note that all of the above minimum, maximum, and default values are
set by the libfstrm library, and may be subject to change in
future versions of the library. See the libfstrm documentation
for more information.
dnstap-output
This configures the path to which the dnstap frame stream is sent
if dnstap is enabled at compile time and active.
The first argument is either file or unix, indicating whether
the destination is a file or a Unix domain socket. The second
argument is the path of the file or socket. (Note: when using a
socket, dnstap messages are only sent if another process such
as fstrm_capture (provided with libfstrm) is listening on the
socket.)
If the first argument is file, then up to three additional
options can be added: size indicates the size to which a
dnstap log file can grow before being rolled to a new file;
versions specifies the number of rolled log files to retain; and
suffix indicates whether to retain rolled log files with an
incrementing counter as the suffix (increment) or with the
current timestamp (timestamp). These are similar to the size,
versions, and suffix options in a logging channel. The
default is to allow dnstap log files to grow to any size without
rolling.
dnstap-output can only be set globally in options. Currently,
it can only be set once while named is running; once set, it
cannot be changed by rndcreload or rndcreconfig.
dnstap-identity
This specifies an identity string to send in dnstap messages. If
set to hostname, which is the default, the server’s hostname
is sent. If set to none, no identity string is sent.
dnstap-version
This specifies a version string to send in dnstap messages. The
default is the version number of the BIND release. If set to
none, no version string is sent.
geoip-directory
When named is compiled using the MaxMind GeoIP2 geolocation API, this
specifies the directory containing GeoIP database files. By default, the
option is set based on the prefix used to build the libmaxminddb module;
for example, if the library is installed in /usr/local/lib, then the
default geoip-directory is /usr/local/share/GeoIP. On Windows,
the default is the named working directory. See acl Statement Definition and Usage
for details about geoip ACLs.
key-directory
This is the directory where the public and private DNSSEC key files should be
found when performing a dynamic update of secure zones, if different
than the current working directory. (Note that this option has no
effect on the paths for files containing non-DNSSEC keys such as
bind.keys, rndc.key, or session.key.)
lmdb-mapsize
When named is built with liblmdb, this option sets a maximum size
for the memory map of the new-zone database (NZD) in LMDB database
format. This database is used to store configuration information for
zones added using rndcaddzone. Note that this is not the NZD
database file size, but the largest size that the database may grow
to.
Because the database file is memory-mapped, its size is limited by
the address space of the named process. The default of 32 megabytes
was chosen to be usable with 32-bit named builds. The largest
permitted value is 1 terabyte. Given typical zone configurations
without elaborate ACLs, a 32 MB NZD file ought to be able to hold
configurations of about 100,000 zones.
managed-keys-directory
This specifies the directory in which to store the files that track managed DNSSEC
keys (i.e., those configured using the initial-key or initial-ds
keywords in a trust-anchors statement). By default, this is the working
directory. The directory must be writable by the effective user ID of the
named process.
If named is not configured to use views, managed keys for
the server are tracked in a single file called
managed-keys.bind. Otherwise, managed keys are tracked in
separate files, one file per view; each file name is the view
name (or, if it contains characters that are incompatible with use as
a file name, the SHA256 hash of the view name), followed by the
extension .mkeys.
(Note: in earlier releases, file names for views always used the
SHA256 hash of the view name. To ensure compatibility after upgrading,
if a file using the old name format is found to exist, it is
used instead of the new format.)
max-ixfr-ratio
This sets the size threshold (expressed as a percentage of the size
of the full zone) beyond which named chooses to use an AXFR
response rather than IXFR when answering zone transfer requests. See
Incremental Zone Transfers (IXFR).
The minimum value is 1%. The keyword unlimited disables ratio
checking and allows IXFRs of any size. The default is unlimited.
new-zones-directory
This specifies the directory in which to store the configuration
parameters for zones added via rndcaddzone. By default, this is
the working directory. If set to a relative path, it is relative
to the working directory. The directory must be writable by the
effective user ID of the named process.
qname-minimization
This option controls QNAME minimization behavior in the BIND
resolver. When set to strict, BIND follows the QNAME
minimization algorithm to the letter, as specified in RFC 7816.
Setting this option to relaxed causes BIND to fall back to
normal (non-minimized) query mode when it receives either NXDOMAIN or
other unexpected responses (e.g., SERVFAIL, improper zone cut,
REFUSED) to a minimized query. disabled disables QNAME
minimization completely. The current default is relaxed, but it
may be changed to strict in a future release.
tkey-gssapi-keytab
This is the KRB5 keytab file to use for GSS-TSIG updates. If this option is
set and tkey-gssapi-credential is not set, updates are
allowed with any key matching a principal in the specified keytab.
tkey-gssapi-credential
This is the security credential with which the server should authenticate
keys requested by the GSS-TSIG protocol. Currently only Kerberos 5
authentication is available; the credential is a Kerberos
principal which the server can acquire through the default system key
file, normally /etc/krb5.keytab. The location of the keytab file can be
overridden using the tkey-gssapi-keytab option. Normally this
principal is of the form DNS/server.domain. To use
GSS-TSIG, tkey-domain must also be set if a specific keytab is
not set with tkey-gssapi-keytab.
tkey-domain
This domain is appended to the names of all shared keys generated with
TKEY. When a client requests a TKEY exchange, it may or may
not specify the desired name for the key. If present, the name of the
shared key is client-specifiedpart + tkey-domain.
Otherwise, the name of the shared key is randomhexdigits
+ tkey-domain. In most cases, the domainname
should be the server’s domain name, or an otherwise nonexistent
subdomain like _tkey.domainname. If using GSS-TSIG,
this variable must be defined, unless a specific keytab
is specified using tkey-gssapi-keytab.
tkey-dhkey
This is the Diffie-Hellman key used by the server to generate shared keys
with clients using the Diffie-Hellman mode of TKEY. The server
must be able to load the public and private keys from files in the
working directory. In most cases, the key_name should be the
server’s host name.
cache-file
This is for testing only. Do not use.
dump-file
This is the pathname of the file the server dumps the database to, when
instructed to do so with rndcdumpdb. If not specified, the
default is named_dump.db.
memstatistics-file
This is the pathname of the file the server writes memory usage statistics to
on exit. If not specified, the default is named.memstats.
lock-file
This is the pathname of a file on which named attempts to acquire a
file lock when starting for the first time; if unsuccessful, the
server terminates, under the assumption that another server
is already running. If not specified, the default is
none.
Specifying lock-filenone disables the use of a lock file.
lock-file is ignored if named was run using the -X
option, which overrides it. Changes to lock-file are ignored if
named is being reloaded or reconfigured; it is only effective
when the server is first started.
pid-file
This is the pathname of the file the server writes its process ID in. If not
specified, the default is /var/run/named/named.pid. The PID file
is used by programs that send signals to the running name
server. Specifying pid-filenone disables the use of a PID file;
no file is written and any existing one is removed. Note
that none is a keyword, not a filename, and therefore is not
enclosed in double quotes.
recursing-file
This is the pathname of the file where the server dumps the queries that are
currently recursing, when instructed to do so with rndcrecursing.
If not specified, the default is named.recursing.
statistics-file
This is the pathname of the file the server appends statistics to, when
instructed to do so using rndcstats. If not specified, the
default is named.stats in the server’s current directory. The
format of the file is described in The Statistics File.
bindkeys-file
This is the pathname of a file to override the built-in trusted keys provided
by named. See the discussion of dnssec-validation for
details. If not specified, the default is /etc/bind.keys.
secroots-file
This is the pathname of the file the server dumps security roots to, when
instructed to do so with rndcsecroots. If not specified, the
default is named.secroots.
session-keyfile
This is the pathname of the file into which to write a TSIG session key
generated by named for use by nsupdate-l. If not specified,
the default is /var/run/named/session.key. (See Dynamic Update Policies,
and in particular the discussion of the update-policy statement’s
local option, for more information about this feature.)
session-keyname
This is the key name to use for the TSIG session key. If not specified, the
default is local-ddns.
session-keyalg
This is the algorithm to use for the TSIG session key. Valid values are
hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, hmac-sha512, and
hmac-md5. If not specified, the default is hmac-sha256.
port
This is the UDP/TCP port number the server uses to receive and send DNS
protocol traffic. The default is 53. This option is mainly intended
for server testing; a server using a port other than 53 is not
able to communicate with the global DNS.
dscp
This is the global Differentiated Services Code Point (DSCP) value to
classify outgoing DNS traffic, on operating systems that support DSCP.
Valid values are 0 through 63. It is not configured by default.
random-device
This specifies a source of entropy to be used by the server; it is a
device or file from which to read entropy. If it is a file,
operations requiring entropy will fail when the file has been
exhausted.
Entropy is needed for cryptographic operations such as TKEY
transactions, dynamic update of signed zones, and generation of TSIG
session keys. It is also used for seeding and stirring the
pseudo-random number generator which is used for less critical
functions requiring randomness, such as generation of DNS message
transaction IDs.
If random-device is not specified, or if it is set to none,
entropy is read from the random number generation function
supplied by the cryptographic library with which BIND was linked
(i.e. OpenSSL or a PKCS#11 provider).
The random-device option takes effect during the initial
configuration load at server startup time and is ignored on
subsequent reloads.
preferred-glue
If specified, the listed type (A or AAAA) is emitted before
other glue in the additional section of a query response. The default
is to prefer A records when responding to queries that arrived via
IPv4 and AAAA when responding to queries that arrived via IPv6.
root-delegation-only
This turns on enforcement of delegation-only in TLDs (top-level domains)
and root zones with an optional exclude list.
DS queries are expected to be made to and be answered by delegation-only
zones. Such queries and responses are treated as an exception to
delegation-only processing and are not converted to NXDOMAIN
responses, provided a CNAME is not discovered at the query name.
If a delegation-only zone server also serves a child zone, it is not
always possible to determine whether an answer comes from the
delegation-only zone or the child zone. SOA NS and DNSKEY records are
apex-only records and a matching response that contains these records
or DS is treated as coming from a child zone. RRSIG records are also
examined to see whether they are signed by a child zone, and the
authority section is examined to see if there is evidence that
the answer is from the child zone. Answers that are determined to be
from a child zone are not converted to NXDOMAIN responses. Despite
all these checks, there is still a possibility of false negatives when
a child zone is being served.
Similarly, false positives can arise from empty nodes (no records at
the name) in the delegation-only zone when the query type is not ANY.
Note that some TLDs are not delegation-only; e.g., “DE”, “LV”, “US”, and
“MUSEUM”. This list is not exhaustive.
This disables the specified DNSSEC algorithms at and below the specified
name. Multiple disable-algorithms statements are allowed. Only
the best-match disable-algorithms clause is used to
determine the algorithms.
If all supported algorithms are disabled, the zones covered by the
disable-algorithms setting are treated as insecure.
Configured trust anchors in trust-anchors (or managed-keys or
trusted-keys) that match a disabled algorithm are ignored and treated
as if they were not configured.
disable-ds-digests
This disables the specified DS digest types at and below the specified
name. Multiple disable-ds-digests statements are allowed. Only
the best-match disable-ds-digests clause is used to
determine the digest types.
If all supported digest types are disabled, the zones covered by
disable-ds-digests are treated as insecure.
dnssec-must-be-secure
This specifies hierarchies which must be or may not be secure (signed and
validated). If yes, then named only accepts answers if
they are secure. If no, then normal DNSSEC validation applies,
allowing insecure answers to be accepted. The specified domain
must be defined as a trust anchor, for instance in a trust-anchors
statement, or dnssec-validationauto must be active.
dns64
This directive instructs named to return mapped IPv4 addresses to
AAAA queries when there are no AAAA records. It is intended to be
used in conjunction with a NAT64. Each dns64 defines one DNS64
prefix. Multiple DNS64 prefixes can be defined.
Compatible IPv6 prefixes have lengths of 32, 40, 48, 56, 64, and 96, per
RFC 6052. Bits 64..71 inclusive must be zero, with the most significant bit
of the prefix in position 0.
In addition, a reverse IP6.ARPA zone is created for the prefix
to provide a mapping from the IP6.ARPA names to the corresponding
IN-ADDR.ARPA names using synthesized CNAMEs. dns64-server and
dns64-contact can be used to specify the name of the server and
contact for the zones. These can be set at the view/options
level but not on a per-prefix basis.
Each dns64 supports an optional clients ACL that determines
which clients are affected by this directive. If not defined, it
defaults to any;.
Each dns64 supports an optional mapped ACL that selects which
IPv4 addresses are to be mapped in the corresponding A RRset. If not
defined, it defaults to any;.
Normally, DNS64 does not apply to a domain name that owns one or more
AAAA records; these records are simply returned. The optional
exclude ACL allows specification of a list of IPv6 addresses that
are ignored if they appear in a domain name’s AAAA records;
DNS64 is applied to any A records the domain name owns. If not
defined, exclude defaults to ::ffff:0.0.0.0/96.
An optional suffix can also be defined to set the bits trailing
the mapped IPv4 address bits. By default these bits are set to
::. The bits matching the prefix and mapped IPv4 address must be
zero.
If recursive-only is set to yes, the DNS64 synthesis only
happens for recursive queries. The default is no.
If break-dnssec is set to yes, the DNS64 synthesis happens
even if the result, if validated, would cause a DNSSEC validation
failure. If this option is set to no (the default), the DO is set
on the incoming query, and there are RRSIGs on the applicable
records, then synthesis does not happen.
When a zone is configured with auto-dnssecmaintain;, its key
repository must be checked periodically to see if any new keys have
been added or any existing keys’ timing metadata has been updated
(see dnssec-keygen: DNSSEC key generation tool and dnssec-settime: set the key timing metadata for a DNSSEC key).
The dnssec-loadkeys-interval option
sets the frequency of automatic repository checks, in minutes. The
default is 60 (1 hour), the minimum is 1 (1 minute), and
the maximum is 1440 (24 hours); any higher value is silently
reduced.
dnssec-policy
This specifies which key and signing policy (KASP) should be used for this
zone. This is a string referring to a dnssec-policy statement. There
are three built-in policies: default, which uses the default policy,
insecure, to be used when you want to gracefully unsign your zone, and
none, which means no DNSSEC policy. The default is none.
See dnssec-policy Grammar for more details.
dnssec-update-mode
If this option is set to its default value of maintain in a zone
of type primary which is DNSSEC-signed and configured to allow
dynamic updates (see Dynamic Update Policies), and if named has access
to the private signing key(s) for the zone, then named
automatically signs all new or changed records and maintains signatures
for the zone by regenerating RRSIG records whenever they approach
their expiration date.
If the option is changed to no-resign, then named signs
all new or changed records, but scheduled maintenance of signatures
is disabled.
With either of these settings, named rejects updates to a
DNSSEC-signed zone when the signing keys are inactive or unavailable
to named. (A planned third option, external, will disable all
automatic signing and allow DNSSEC data to be submitted into a zone
via dynamic update; this is not yet implemented.)
nta-lifetime
This specifies the default lifetime, in seconds, for
negative trust anchors added via rndcnta.
A negative trust anchor selectively disables DNSSEC validation for
zones that are known to be failing because of misconfiguration, rather
than an attack. When data to be validated is at or below an active
NTA (and above any other configured trust anchors), named
aborts the DNSSEC validation process and treats the data as insecure
rather than bogus. This continues until the NTA’s lifetime has
elapsed. NTAs persist across named restarts.
For convenience, TTL-style time-unit suffixes can be used to specify the NTA
lifetime in seconds, minutes, or hours. It also accepts ISO 8601 duration
formats.
nta-lifetime defaults to one hour; it cannot exceed one week.
nta-recheck
This specifies how often to check whether negative trust anchors added via
rndcnta are still necessary.
A negative trust anchor is normally used when a domain has stopped
validating due to operator error; it temporarily disables DNSSEC
validation for that domain. In the interest of ensuring that DNSSEC
validation is turned back on as soon as possible, named
periodically sends a query to the domain, ignoring negative trust
anchors, to find out whether it can now be validated. If so, the
negative trust anchor is allowed to expire early.
Validity checks can be disabled for an individual NTA by using
rndcnta-f, or for all NTAs by setting nta-recheck to zero.
For convenience, TTL-style time-unit suffixes can be used to specify the NTA
recheck interval in seconds, minutes, or hours. It also accepts ISO 8601
duration formats.
The default is five minutes. It cannot be longer than nta-lifetime, which
cannot be longer than a week.
max-zone-ttl
This should now be configured as part of dnssec-policy.
Use of this option in options, view and zone blocks has no
effect on any zone for which a dnssec-policy has also been configured.
max-zone-ttl specifies a maximum permissible TTL value in seconds.
For convenience, TTL-style time-unit suffixes may be used to specify the
maximum value. When a zone file is loaded, any record encountered with a
TTL higher than max-zone-ttl causes the zone to be rejected.
This is useful in DNSSEC-signed zones because when rolling to a new
DNSKEY, the old key needs to remain available until RRSIG records
have expired from caches. The max-zone-ttl option guarantees that
the largest TTL in the zone is no higher than the set value.
(Note: because map-format files load directly into memory, this
option cannot be used with them.)
The default value is unlimited. Setting max-zone-ttl to zero is
equivalent to unlimited.
stale-answer-ttl
This specifies the TTL to be returned on stale answers. The default is 30
seconds. The minimum allowed is 1 second; a value of 0 is updated silently
to 1 second.
For stale answers to be returned, they must be enabled, either in the
configuration file using stale-answer-enable or via
rndcserve-staleon.
serial-update-method
Zones configured for dynamic DNS may use this option to set the
update method to be used for the zone serial number in the SOA
record.
With the default setting of serial-update-methodincrement;, the
SOA serial number is incremented by one each time the zone is
updated.
When set to serial-update-methodunixtime;, the SOA serial number
is set to the number of seconds since the Unix epoch, unless the
serial number is already greater than or equal to that value, in
which case it is simply incremented by one.
When set to serial-update-methoddate;, the new SOA serial number
is the current date in the form “YYYYMMDD”, followed by two
zeroes, unless the existing serial number is already greater than or
equal to that value, in which case it is incremented by one.
zone-statistics
If full, the server collects statistical data on all zones,
unless specifically turned off on a per-zone basis by specifying
zone-statisticsterse or zone-statisticsnone in the zone
statement. The statistical data includes, for example, DNSSEC signing
operations and the number of authoritative answers per query type. The
default is terse, providing minimal statistics on zones
(including name and current serial number, but not query type
counters).
These statistics may be accessed via the statistics-channel or
using rndcstats, which dumps them to the file listed in the
statistics-file. See also The Statistics File.
For backward compatibility with earlier versions of BIND 9, the
zone-statistics option can also accept yes or no; yes
has the same meaning as full. As of BIND 9.10, no has the
same meaning as none; previously, it was the same as terse.
If yes and supported by the operating system, this automatically rescans
network interfaces when the interface addresses are added or removed. The
default is yes. This configuration option does not affect the time-based
interface-interval option; it is recommended to set the time-based
interface-interval to 0 when the operator confirms that automatic
interface scanning is supported by the operating system.
The automatic-interface-scan implementation uses routing sockets for the
network interface discovery; therefore, the operating system must
support the routing sockets for this feature to work.
allow-new-zones
If yes, then zones can be added at runtime via rndcaddzone.
The default is no.
Newly added zones’ configuration parameters are stored so that they
can persist after the server is restarted. The configuration
information is saved in a file called viewname.nzf (or, if
named is compiled with liblmdb, in an LMDB database file called
viewname.nzd). “viewname” is the name of the view, unless the view
name contains characters that are incompatible with use as a file
name, in which case a cryptographic hash of the view name is used
instead.
Configurations for zones added at runtime are stored either in
a new-zone file (NZF) or a new-zone database (NZD), depending on
whether named was linked with liblmdb at compile time. See
rndc - name server control utility for further details about rndcaddzone.
auth-nxdomain
If yes, then the AA bit is always set on NXDOMAIN responses,
even if the server is not actually authoritative. The default is
no.
memstatistics
This writes memory statistics to the file specified by
memstatistics-file at exit. The default is no unless -mrecord is specified on the command line, in which case it is yes.
dialup
If yes, then the server treats all zones as if they are doing
zone transfers across a dial-on-demand dialup link, which can be
brought up by traffic originating from this server. Although this setting has
different effects according to zone type, it concentrates the zone
maintenance so that everything happens quickly, once every
heartbeat-interval, ideally during a single call. It also
suppresses some normal zone maintenance traffic. The default
is no.
If specified in the view and
zone statements, the dialup option overrides the global dialup
option.
If the zone is a primary zone, the server sends out a NOTIFY
request to all the secondaries (default). This should trigger the zone
serial number check in the secondary (providing it supports NOTIFY),
allowing the secondary to verify the zone while the connection is active.
The set of servers to which NOTIFY is sent can be controlled by
notify and also-notify.
If the zone is a secondary or stub zone, the server suppresses
the regular “zone up to date” (refresh) queries and only performs them
when the heartbeat-interval expires, in addition to sending NOTIFY
requests.
Finer control can be achieved by using notify, which only sends
NOTIFY messages; notify-passive, which sends NOTIFY messages and
suppresses the normal refresh queries; refresh, which suppresses
normal refresh processing and sends refresh queries when the
heartbeat-interval expires; and passive, which disables
normal refresh processing.
dialup mode
normal refresh
heart-beat
refresh
heart-beat
notify
no
(default)
yes
no
no
yes
no
yes
yes
notify
yes
no
yes
refresh
no
yes
no
passive
no
no
no
notify-passive
no
no
yes
Note that normal NOTIFY processing is not affected by dialup.
flush-zones-on-shutdown
When the name server exits upon receiving SIGTERM, flush or do not
flush any pending zone writes. The default is
flush-zones-on-shutdownno.
geoip-use-ecs
This option was part of an experimental implementation of the EDNS
CLIENT-SUBNET for authoritative servers, but is now obsolete.
root-key-sentinel
If yes, respond to root key sentinel probes as described in
draft-ietf-dnsop-kskroll-sentinel-08. The default is yes.
reuseport
This option enables kernel load-balancing of sockets on systems which support
it, including Linux (SO_REUSEPORT) and FreeBSD (SO_REUSEPORT_LB). This
instructs the kernel to distribute incoming socket connections among the
networking threads based on a hashing scheme. For more information, see the
receive network flow classification options (rx-flow-hash) section in the
ethtool manual page. The default is yes.
Enabling reuseport significantly increases general throughput when
incoming traffic is distributed uniformly onto the threads by the
operating system. However, in cases where a worker thread is busy with a
long-lasting operation, such as processing a Response Policy Zone (RPZ) or
Catalog Zone update or an unusually large zone transfer, incoming traffic
that hashes onto that thread may be delayed. On servers where these events
occur frequently, it may be preferable to disable socket load-balancing so
that other threads can pick up the traffic that would have been sent to the
busy thread.
Note: this option can only be set when named first starts.
Changes will not take effect during reconfiguration; the server
must be restarted.
message-compression
If yes, DNS name compression is used in responses to regular
queries (not including AXFR or IXFR, which always use compression).
Setting this option to no reduces CPU usage on servers and may
improve throughput. However, it increases response size, which may
cause more queries to be processed using TCP; a server with
compression disabled is out of compliance with RFC 1123 Section
6.1.3.2. The default is yes.
minimal-responses
This option controls the addition of records to the authority and
additional sections of responses. Such records may be included in
responses to be helpful to clients; for example, MX records may
have associated address records included in the additional section,
obviating the need for a separate address lookup. However, adding
these records to responses is not mandatory and requires additional
database lookups, causing extra latency when marshalling responses.
Responses to DNSKEY, DS, CDNSKEY, and CDS requests will never have
optional additional records added. Responses to NS requests will
always have additional section processing.
minimal-responses takes one of four values:
no: the server is as complete as possible when generating
responses.
yes: the server only adds records to the authority and additional
sections when such records are required by the DNS protocol (for
example, when returning delegations or negative responses). This
provides the best server performance but may result in more client
queries.
no-auth: the server omits records from the authority section except
when they are required, but it may still add records to the
additional section.
no-auth-recursive: the same as no-auth when recursion is requested
in the query (RD=1), or the same as no if recursion is not requested.
no-auth and no-auth-recursive are useful when answering stub
clients, which usually ignore the authority section.
no-auth-recursive is meant for use in mixed-mode servers that
handle both authoritative and recursive queries.
The default is no-auth-recursive.
glue-cache
When set to yes, a cache is used to improve query performance
when adding address-type (A and AAAA) glue records to the additional
section of DNS response messages that delegate to a child zone.
The glue cache uses memory proportional to the number of delegations
in the zone. The default setting is yes, which improves
performance at the cost of increased memory usage for the zone. To avoid
this, set it to no.
minimal-any
If set to yes, the server replies with only one of
the RRsets for the query name, and its covering RRSIGs if any,
when generating a positive response to a query of type ANY over UDP,
instead of replying with all known RRsets for the name. Similarly, a
query for type RRSIG is answered with the RRSIG records covering
only one type. This can reduce the impact of some kinds of attack
traffic, without harming legitimate clients. (Note, however, that the
RRset returned is the first one found in the database; it is not
necessarily the smallest available RRset.) Additionally,
minimal-responses is turned on for these queries, so no
unnecessary records are added to the authority or additional
sections. The default is no.
notify
If set to yes (the default), DNS NOTIFY messages are sent when a
zone the server is authoritative for changes; see Notify.
The messages are sent to the servers listed in the zone’s NS records
(except the primary server identified in the SOA MNAME field), and to
any servers listed in the also-notify option.
If set to primary-only (or the older keyword master-only),
notifies are only sent for primary zones. If set to explicit,
notifies are sent only to servers explicitly listed using
also-notify. If set to no, no notifies are sent.
The notify option may also be specified in the zone
statement, in which case it overrides the optionsnotify
statement. It would only be necessary to turn off this option if it
caused secondary zones to crash.
notify-to-soa
If yes, do not check the name servers in the NS RRset against the
SOA MNAME. Normally a NOTIFY message is not sent to the SOA MNAME
(SOA ORIGIN), as it is supposed to contain the name of the ultimate
primary server. Sometimes, however, a secondary server is listed as the SOA MNAME in
hidden primary configurations; in that case, the
ultimate primary should be set to still send NOTIFY messages to all the name servers
listed in the NS RRset.
recursion
If yes, and a DNS query requests recursion, then the server
attempts to do all the work required to answer the query. If recursion
is off and the server does not already know the answer, it
returns a referral response. The default is yes. Note that setting
recursionno does not prevent clients from getting data from the
server’s cache; it only prevents new data from being cached as an
effect of client queries. Caching may still occur as an effect of the
server’s internal operation, such as NOTIFY address lookups.
request-nsid
If yes, then an empty EDNS(0) NSID (Name Server Identifier)
option is sent with all queries to authoritative name servers during
iterative resolution. If the authoritative server returns an NSID
option in its response, then its contents are logged in the nsid
category at level info. The default is no.
request-sit
This experimental option is obsolete.
require-server-cookie
If yes, require a valid server cookie before sending a full response to a UDP
request from a cookie-aware client. BADCOOKIE is sent if there is a
bad or nonexistent server cookie.
The default is no.
Users wishing to test that DNS COOKIE clients correctly handle
BADCOOKIE, or who are getting a lot of forged DNS requests with DNS COOKIES
present, should set this to yes. Setting this to yes results in a reduced amplification effect
in a reflection attack, as the BADCOOKIE response is smaller than a full
response, while also requiring a legitimate client to follow up with a second
query with the new, valid, cookie.
answer-cookie
When set to the default value of yes, COOKIE EDNS options are
sent when applicable in replies to client queries. If set to no,
COOKIE EDNS options are not sent in replies. This can only be set
at the global options level, not per-view.
answer-cookieno is intended as a temporary measure, for use when
named shares an IP address with other servers that do not yet
support DNS COOKIE. A mismatch between servers on the same address is
not expected to cause operational problems, but the option to disable
COOKIE responses so that all servers have the same behavior is
provided out of an abundance of caution. DNS COOKIE is an important
security mechanism, and should not be disabled unless absolutely
necessary.
send-cookie
If yes, then a COOKIE EDNS option is sent along with the query.
If the resolver has previously communicated with the server, the COOKIE
returned in the previous transaction is sent. This is used by the
server to determine whether the resolver has talked to it before. A
resolver sending the correct COOKIE is assumed not to be an off-path
attacker sending a spoofed-source query; the query is therefore
unlikely to be part of a reflection/amplification attack, so
resolvers sending a correct COOKIE option are not subject to response
rate limiting (RRL). Resolvers which do not send a correct COOKIE
option may be limited to receiving smaller responses via the
nocookie-udp-size option.
The default is yes.
stale-answer-enable
If yes, enable the returning of “stale” cached answers when the name
servers for a zone are not answering and the stale-cache-enable option is
also enabled. The default is not to return stale answers.
Stale answers can also be enabled or disabled at runtime via
rndcserve-staleon or rndcserve-staleoff; these override
the configured setting. rndcserve-stalereset restores the
setting to the one specified in named.conf. Note that if stale
answers have been disabled by rndc, they cannot be
re-enabled by reloading or reconfiguring named; they must be
re-enabled with rndcserve-staleon, or the server must be
restarted.
Information about stale answers is logged under the serve-stale
log category.
stale-answer-client-timeout
This option defines the amount of time (in milliseconds) that named
waits before attempting to answer the query with a stale RRset from cache.
If a stale answer is found, named continues the ongoing fetches,
attempting to refresh the RRset in cache until the
resolver-query-timeout interval is reached.
This option is off by default, which is equivalent to setting it to
off or disabled. It also has no effect if stale-answer-enable
is disabled.
The maximum value for this option is resolver-query-timeout minus
one second. The minimum value, 0, causes a cached (stale) RRset to be
immediately returned if it is available while still attempting to
refresh the data in cache. RFC 8767 recommends a value of 1800
(milliseconds).
stale-cache-enable
If yes, enable the retaining of “stale” cached answers. Default yes.
stale-refresh-time
If the name servers for a given zone are not answering, this sets the time
window for which named will promptly return “stale” cached answers for
that RRSet being requested before a new attempt in contacting the servers
is made. For convenience, TTL-style time-unit suffixes may be used to
specify the value. It also accepts ISO 8601 duration formats.
The default stale-refresh-time is 30 seconds, as RFC 8767 recommends
that attempts to refresh to be done no more frequently than every 30
seconds. A value of zero disables the feature, meaning that normal
resolution will take place first, if that fails only then named will
return “stale” cached answers.
nocookie-udp-size
This sets the maximum size of UDP responses that are sent to queries
without a valid server COOKIE. A value below 128 is silently
raised to 128. The default value is 4096, but the max-udp-size
option may further limit the response size as the default for
max-udp-size is 4096.
sit-secret
This experimental option is obsolete.
cookie-algorithm
This sets the algorithm to be used when generating the server cookie; the options are
“aes” or “siphash24”. The default is “siphash24”. The “aes” option remains for legacy
purposes.
cookie-secret
If set, this is a shared secret used for generating and verifying
EDNS COOKIE options within an anycast cluster. If not set, the system
generates a random secret at startup. The shared secret is
encoded as a hex string and needs to be 128 bits for either “siphash24”
or “aes”.
If there are multiple secrets specified, the first one listed in
named.conf is used to generate new server cookies. The others
are only used to verify returned cookies.
response-padding
The EDNS Padding option is intended to improve confidentiality when
DNS queries are sent over an encrypted channel, by reducing the
variability in packet sizes. If a query:
contains an EDNS Padding option,
includes a valid server cookie or uses TCP,
is not signed using TSIG or SIG(0), and
is from a client whose address matches the specified ACL,
then the response is padded with an EDNS Padding option to a multiple
of block-size bytes. If these conditions are not met, the
response is not padded.
If block-size is 0 or the ACL is none;, this feature is
disabled and no padding occurs; this is the default. If
block-size is greater than 512, a warning is logged and the value
is truncated to 512. Block sizes are ordinarily expected to be powers
of two (for instance, 128), but this is not mandatory.
trust-anchor-telemetry
This causes named to send specially formed queries once per day to
domains for which trust anchors have been configured via, e.g.,
trust-anchors or dnssec-validationauto.
The query name used for these queries has the form
_ta-xxxx(-xxxx)(...).<domain>, where each “xxxx” is a group of four
hexadecimal digits representing the key ID of a trusted DNSSEC key.
The key IDs for each domain are sorted smallest to largest prior to
encoding. The query type is NULL.
By monitoring these queries, zone operators are able to see which
resolvers have been updated to trust a new key; this may help them
decide when it is safe to remove an old one.
If yes, then an IPv4-mapped IPv6 address matches any
address-match list entries that match the corresponding IPv4 address.
This option was introduced to work around a kernel quirk in some
operating systems that causes IPv4 TCP connections, such as zone
transfers, to be accepted on an IPv6 socket using mapped addresses.
This caused address-match lists designed for IPv4 to fail to match.
However, named now solves this problem internally. The use of
this option is discouraged.
ixfr-from-differences
When yes and the server loads a new version of a primary zone from
its zone file or receives a new version of a secondary file via zone
transfer, it compares the new version to the previous one and
calculates a set of differences. The differences are then logged in
the zone’s journal file so that the changes can be transmitted to
downstream secondaries as an incremental zone transfer.
By allowing incremental zone transfers to be used for non-dynamic
zones, this option saves bandwidth at the expense of increased CPU
and memory consumption at the primary server. In particular, if the new
version of a zone is completely different from the previous one, the
set of differences is of a size comparable to the combined size
of the old and new zone versions, and the server needs to
temporarily allocate memory to hold this complete difference set.
ixfr-from-differences also accepts primary
and secondary at the view and options levels,
which causes ixfr-from-differences to be enabled for all primary
or secondary zones, respectively. It is off for all zones by default.
Note: if inline signing is enabled for a zone, the user-provided
ixfr-from-differences setting is ignored for that zone.
multi-master
This should be set when there are multiple primary servers for a zone and the
addresses refer to different machines. If yes, named does not
log when the serial number on the primary is less than what named
currently has. The default is no.
auto-dnssec
Zones configured for dynamic DNS may use this option to allow varying
levels of automatic DNSSEC key management. There are three possible
settings:
auto-dnssecallow; permits keys to be updated and the zone fully
re-signed whenever the user issues the command rndcsignzonename.
auto-dnssecmaintain; includes the above, but also
automatically adjusts the zone’s DNSSEC keys on a schedule, according
to the keys’ timing metadata (see dnssec-keygen: DNSSEC key generation tool and
dnssec-settime: set the key timing metadata for a DNSSEC key). The command rndcsignzonename
causes named to load keys from the key repository and sign the
zone with all keys that are active. rndcloadkeyszonename
causes named to load keys from the key repository and schedule
key maintenance events to occur in the future, but it does not sign
the full zone immediately. Note: once keys have been loaded for a
zone the first time, the repository is searched for changes
periodically, regardless of whether rndcloadkeys is used. The
recheck interval is defined by dnssec-loadkeys-interval.
auto-dnssecoff; does not allow for DNSSEC key management.
This is the default setting.
This option may only be activated at the zone level; if configured
at the view or options level, it must be set to off.
The DNSSEC records are written to the zone’s filename set in file,
unless inline-signing is enabled.
dnssec-enable
This option is obsolete and has no effect.
dnssec-validation
This option enables DNSSEC validation in named.
If set to auto, DNSSEC validation is enabled and a default trust
anchor for the DNS root zone is used. This trust anchor is provided
as part of BIND and is kept up-to-date using Dynamic Trust Anchor Management key
management.
If set to yes, DNSSEC validation is enabled, but a trust anchor must be
manually configured using a trust-anchors statement (or the
managed-keys or trusted-keys statements, both deprecated). If
there is no configured trust anchor, validation does not take place.
If set to no, DNSSEC validation is disabled.
The default is auto, unless BIND is built with
configure--disable-auto-validation, in which case the default is
yes.
The default root trust anchor is stored in the file bind.keys.
named loads that key at startup if dnssec-validation is
set to auto. A copy of the file is installed along with BIND 9,
and is current as of the release date. If the root key expires, a new
copy of bind.keys can be downloaded from
https://www.isc.org/bind-keys.
(To prevent problems if bind.keys is not found, the current trust
anchor is also compiled in named. Relying on this is not
recommended, however, as it requires named to be recompiled with
a new key when the root key expires.)
Note
named loads only the root key from bind.keys. The file
cannot be used to store keys for other zones. The root key in
bind.keys is ignored if dnssec-validationauto is not in
use.
Whenever the resolver sends out queries to an EDNS-compliant
server, it always sets the DO bit indicating it can support DNSSEC
responses, even if dnssec-validation is off.
validate-except
This specifies a list of domain names at and beneath which DNSSEC
validation should not be performed, regardless of the presence of a
trust anchor at or above those names. This may be used, for example,
when configuring a top-level domain intended only for local use, so
that the lack of a secure delegation for that domain in the root zone
does not cause validation failures. (This is similar to setting a
negative trust anchor except that it is a permanent configuration,
whereas negative trust anchors expire and are removed after a set
period of time.)
dnssec-accept-expired
This accepts expired signatures when verifying DNSSEC signatures. The
default is no. Setting this option to yes leaves named
vulnerable to replay attacks.
querylog
Query logging provides a complete log of all incoming queries and all query
errors. This provides more insight into the server’s activity, but with a
cost to performance which may be significant on heavily loaded servers.
The querylog option specifies whether query logging should be active when
named first starts. If querylog is not specified, then query logging
is determined by the presence of the logging category queries. Query
logging can also be activated at runtime using the command rndcquerylogon, or deactivated with rndcquerylogoff.
check-names
This option is used to restrict the character set and syntax of
certain domain names in primary files and/or DNS responses received
from the network. The default varies according to usage area. For
primary zones the default is fail. For secondary zones the
default is warn. For answers received from the network
(response), the default is ignore.
The rules for legal hostnames and mail domains are derived from
RFC 952 and RFC 821 as modified by RFC 1123.
check-names applies to the owner names of A, AAAA, and MX records.
It also applies to the domain names in the RDATA of NS, SOA, MX, and
SRV records. It further applies to the RDATA of PTR records where the
owner name indicates that it is a reverse lookup of a hostname (the
owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
check-dup-records
This checks primary zones for records that are treated as different by
DNSSEC but are semantically equal in plain DNS. The default is to
warn. Other possible values are fail and ignore.
check-mx
This checks whether the MX record appears to refer to an IP address. The
default is to warn. Other possible values are fail and
ignore.
check-wildcard
This option is used to check for non-terminal wildcards. The use of
non-terminal wildcards is almost always as a result of a lack of
understanding of the wildcard matching algorithm (RFC 1034). This option
affects primary zones. The default (yes) is to check for
non-terminal wildcards and issue a warning.
check-integrity
This performs post-load zone integrity checks on primary zones. It checks
that MX and SRV records refer to address (A or AAAA) records and that
glue address records exist for delegated zones. For MX and SRV
records, only in-zone hostnames are checked (for out-of-zone hostnames,
use named-checkzone). For NS records, only names below top-of-zone
are checked (for out-of-zone names and glue consistency checks, use
named-checkzone). The default is yes.
The use of the SPF record to publish Sender Policy Framework is
deprecated, as the migration from using TXT records to SPF records was
abandoned. Enabling this option also checks that a TXT Sender Policy
Framework record exists (starts with “v=spf1”) if there is an SPF
record. Warnings are emitted if the TXT record does not exist; they can
be suppressed with check-spf.
check-mx-cname
If check-integrity is set, then fail, warn, or ignore MX records
that refer to CNAMES. The default is to warn.
check-srv-cname
If check-integrity is set, then fail, warn, or ignore SRV records
that refer to CNAMES. The default is to warn.
check-sibling
When performing integrity checks, also check that sibling glue
exists. The default is yes.
check-spf
If check-integrity is set, check that there is a TXT Sender
Policy Framework record present (starts with “v=spf1”) if there is an
SPF record present. The default is warn.
zero-no-soa-ttl
If yes, when returning authoritative negative responses to SOA queries, set
the TTL of the SOA record returned in the authority section to zero.
The default is yes.
zero-no-soa-ttl-cache
If yes, when caching a negative response to an SOA query set the TTL to zero.
The default is no.
update-check-ksk
When set to the default value of yes, check the KSK bit in each
key to determine how the key should be used when generating RRSIGs
for a secure zone.
Ordinarily, zone-signing keys (that is, keys without the KSK bit set)
are used to sign the entire zone, while key-signing keys (keys with
the KSK bit set) are only used to sign the DNSKEY RRset at the zone
apex. However, if this option is set to no, then the KSK bit is
ignored; KSKs are treated as if they were ZSKs and are used to sign
the entire zone. This is similar to the dnssec-signzone-z
command-line option.
When this option is set to yes, there must be at least two active
keys for every algorithm represented in the DNSKEY RRset: at least
one KSK and one ZSK per algorithm. If there is any algorithm for
which this requirement is not met, this option is ignored for
that algorithm.
dnssec-dnskey-kskonly
When this option and update-check-ksk are both set to yes,
only key-signing keys (that is, keys with the KSK bit set) are
used to sign the DNSKEY, CDNSKEY, and CDS RRsets at the zone apex.
Zone-signing keys (keys without the KSK bit set) are used to sign
the remainder of the zone, but not the DNSKEY RRset. This is similar
to the dnssec-signzone-x command-line option.
The default is no. If update-check-ksk is set to no, this
option is ignored.
try-tcp-refresh
If yes, try to refresh the zone using TCP if UDP queries fail. The default is
yes.
dnssec-secure-to-insecure
This allows a dynamic zone to transition from secure to insecure (i.e.,
signed to unsigned) by deleting all of the DNSKEY records. The
default is no. If set to yes, and if the DNSKEY RRset at the
zone apex is deleted, all RRSIG and NSEC records are removed from
the zone as well.
If the zone uses NSEC3, it is also necessary to delete the
NSEC3PARAM RRset from the zone apex; this causes the removal of
all corresponding NSEC3 records. (It is expected that this
requirement will be eliminated in a future release.)
Note that if a zone has been configured with auto-dnssecmaintain
and the private keys remain accessible in the key repository,
the zone will be automatically signed again the next time named
is started.
synth-from-dnssec
This option synthesizes answers from cached NSEC, NSEC3, and other RRsets that have been
proved to be correct using DNSSEC. The default is no, but it will become
yes again in future releases.
Note
DNSSEC validation must be enabled for this option to be effective.
This initial implementation only covers synthesis of answers from
NSEC records; synthesis from NSEC3 is planned for the future. This
will also be controlled by synth-from-dnssec.
The forwarding facility can be used to create a large site-wide cache on
a few servers, reducing traffic over links to external name servers. It
can also be used to allow queries by servers that do not have direct
access to the Internet, but wish to look up exterior names anyway.
Forwarding occurs only on those queries for which the server is not
authoritative and does not have the answer in its cache.
forward
This option is only meaningful if the forwarders list is not empty. A
value of first is the default and causes the server to query the
forwarders first; if that does not answer the question, the
server then looks for the answer itself. If only is
specified, the server only queries the forwarders.
forwarders
This specifies a list of IP addresses to which queries are forwarded. The
default is the empty list (no forwarding). Each address in the list can be
associated with an optional port number and/or DSCP value, and a default port
number and DSCP value can be set for the entire list.
Forwarding can also be configured on a per-domain basis, allowing for
the global forwarding options to be overridden in a variety of ways.
Particular domains can be set to use different forwarders, or have a
different forwardonly/first behavior, or not forward at all; see
zone Statement Grammar.
Dual-stack servers are used as servers of last resort, to work around
problems in reachability due to the lack of support for either IPv4 or IPv6
on the host machine.
dual-stack-servers
This specifies host names or addresses of machines with access to both
IPv4 and IPv6 transports. If a hostname is used, the server must be
able to resolve the name using only the transport it has. If the
machine is dual-stacked, the dual-stack-servers parameter has no
effect unless access to a transport has been disabled on the command
line (e.g., named-4).
Access to the server can be restricted based on the IP address of the
requesting system. See Address Match Lists
for details on how to specify IP address lists.
allow-notify
This ACL specifies which hosts may send NOTIFY messages to inform
this server of changes to zones for which it is acting as a secondary
server. This is only applicable for secondary zones (i.e., type
secondary or slave).
If this option is set in view or options, it is globally
applied to all secondary zones. If set in the zone statement, the
global value is overridden.
If not specified, the default is to process NOTIFY messages only from
the configured primaries for the zone. allow-notify can be used
to expand the list of permitted hosts, not to reduce it.
allow-query
This specifies which hosts are allowed to ask ordinary DNS questions.
allow-query may also be specified in the zone statement, in
which case it overrides the optionsallow-query statement. If not
specified, the default is to allow queries from all hosts.
Note
allow-query-cache is used to specify access to the cache.
allow-query-on
This specifies which local addresses can accept ordinary DNS questions.
This makes it possible, for instance, to allow queries on
internal-facing interfaces but disallow them on external-facing ones,
without necessarily knowing the internal network’s addresses.
Note that allow-query-on is only checked for queries that are
permitted by allow-query. A query must be allowed by both ACLs,
or it is refused.
allow-query-on may also be specified in the zone statement,
in which case it overrides the optionsallow-query-on statement.
If not specified, the default is to allow queries on all addresses.
Note
allow-query-cache is used to specify access to the cache.
allow-query-cache
This specifies which hosts are allowed to get answers from the cache. If
allow-recursion is not set, BIND checks to see if the following parameters
are set, in order: allow-query-cache and allow-query (unless recursionno; is set).
If neither of those parameters is set, the default (localnets; localhost;) is used.
allow-query-cache-on
This specifies which local addresses can send answers from the cache. If
allow-query-cache-on is not set, then allow-recursion-on is
used if set. Otherwise, the default is to allow cache responses to be
sent from any address. Note: both allow-query-cache and
allow-query-cache-on must be satisfied before a cache response
can be sent; a client that is blocked by one cannot be allowed by the
other.
allow-recursion
This specifies which hosts are allowed to make recursive queries through
this server. BIND checks to see if the following parameters are set, in
order: allow-query-cache and allow-query. If neither of those parameters
is set, the default (localnets; localhost;) is used.
allow-recursion-on
This specifies which local addresses can accept recursive queries. If
allow-recursion-on is not set, then allow-query-cache-on is
used if set; otherwise, the default is to allow recursive queries on
all addresses. Any client permitted to send recursive queries can
send them to any address on which named is listening. Note: both
allow-recursion and allow-recursion-on must be satisfied
before recursion is allowed; a client that is blocked by one cannot
be allowed by the other.
allow-update
When set in the zone statement for a primary zone, this specifies which
hosts are allowed to submit Dynamic DNS updates to that zone. The
default is to deny updates from all hosts.
Note that allowing updates based on the requestor’s IP address is
insecure; see Dynamic Update Security for details.
In general, this option should only be set at the zone level.
While a default value can be set at the options or view level
and inherited by zones, this could lead to some zones unintentionally
allowing updates.
Updates are written to the zone’s filename that is set in file.
allow-update-forwarding
When set in the zone statement for a secondary zone, this specifies which
hosts are allowed to submit Dynamic DNS updates and have them be
forwarded to the primary. The default is {none;}, which means
that no update forwarding is performed.
To enable update forwarding, specify
allow-update-forwarding{any;}; in the zone statement.
Specifying values other than {none;} or {any;} is usually
counterproductive; the responsibility for update access control
should rest with the primary server, not the secondary.
Note that enabling the update forwarding feature on a secondary server
may expose primary servers to attacks if they rely on insecure
IP-address-based access control; see Dynamic Update Security for more details.
In general this option should only be set at the zone level.
While a default value can be set at the options or view level
and inherited by zones, this can lead to some zones unintentionally
forwarding updates.
allow-transfer
This specifies which hosts are allowed to receive zone transfers from the
server. allow-transfer may also be specified in the zone
statement, in which case it overrides the allow-transfer
statement set in options or view. If not specified, the
default is to allow transfers to all hosts.
blackhole
This specifies a list of addresses which the server does not accept queries
from or use to resolve a query. Queries from these addresses are not
responded to. The default is none.
keep-response-order
This specifies a list of addresses to which the server sends responses
to TCP queries, in the same order in which they were received. This
disables the processing of TCP queries in parallel. The default is
none.
no-case-compress
This specifies a list of addresses which require responses to use
case-insensitive compression. This ACL can be used when named
needs to work with clients that do not comply with the requirement in
RFC 1034 to use case-insensitive name comparisons when checking for
matching domain names.
If left undefined, the ACL defaults to none: case-insensitive
compression is used for all clients. If the ACL is defined and
matches a client, case is ignored when compressing domain
names in DNS responses sent to that client.
This can result in slightly smaller responses; if a response contains
the names “example.com” and “example.COM”, case-insensitive
compression treats the second one as a duplicate. It also
ensures that the case of the query name exactly matches the case of
the owner names of returned records, rather than matches the case of
the records entered in the zone file. This allows responses to
exactly match the query, which is required by some clients due to
incorrect use of case-sensitive comparisons.
Case-insensitive compression is always used in AXFR and IXFR
responses, regardless of whether the client matches this ACL.
There are circumstances in which named does not preserve the case
of owner names of records: if a zone file defines records of
different types with the same name, but the capitalization of the
name is different (e.g., “www.example.com/A” and
“WWW.EXAMPLE.COM/AAAA”), then all responses for that name use
the first version of the name that was used in the zone file. This
limitation may be addressed in a future release. However, domain
names specified in the rdata of resource records (i.e., records of
type NS, MX, CNAME, etc.) always have their case preserved unless
the client matches this ACL.
resolver-query-timeout
This is the amount of time in milliseconds that the resolver spends
attempting to resolve a recursive query before failing. The default
and minimum is 10000 and the maximum is 30000. Setting it to
0 results in the default being used.
This value was originally specified in seconds. Values less than or
equal to 300 are treated as seconds and converted to
milliseconds before applying the above limits.
The interfaces and ports that the server answers queries from may be
specified using the listen-on option. listen-on takes an
optional port and an address_match_list of IPv4 addresses. (IPv6
addresses are ignored, with a logged warning.) The server listens on
all interfaces allowed by the address match list. If a port is not
specified, port 53 is used.
Multiple listen-on statements are allowed. For example:
enables the name server on port 53 for the IP address 5.6.7.8, and
on port 1234 of an address on the machine in net 1.2 that is not
1.2.3.4.
If no listen-on is specified, the server listens on port 53 on
all IPv4 interfaces.
The listen-on-v6 option is used to specify the interfaces and the
ports on which the server listens for incoming queries sent using
IPv6. If not specified, the server listens on port 53 on all IPv6
interfaces.
Multiple listen-on-v6 options can be used. For example:
enables the name server on port 53 for any IPv6 addresses (with a
single wildcard socket), and on port 1234 of IPv6 addresses that are not
in the prefix 2001:db8::/32 (with separate sockets for each matched
address).
To instruct the server not to listen on any IPv6 address, use:
If the server does not know the answer to a question, it queries other
name servers. query-source specifies the address and port used for
such queries. For queries sent over IPv6, there is a separate
query-source-v6 option. If address is * (asterisk) or is
omitted, a wildcard IP address (INADDR_ANY) is used.
If port is * or is omitted, a random port number from a
pre-configured range is picked up and used for each query. The
port range(s) is specified in the use-v4-udp-ports (for IPv4)
and use-v6-udp-ports (for IPv6) options, excluding the ranges
specified in the avoid-v4-udp-ports and avoid-v6-udp-ports
options, respectively.
The defaults of the query-source and query-source-v6 options
are:
If use-v4-udp-ports or use-v6-udp-ports is unspecified,
named checks whether the operating system provides a programming
interface to retrieve the system’s default range for ephemeral ports. If
such an interface is available, named uses the corresponding
system default range; otherwise, it uses its own defaults:
Make sure the ranges are sufficiently large for security. A
desirable size depends on several parameters, but we generally recommend
it contain at least 16384 ports (14 bits of entropy). Note also that the
system’s default range when used may be too small for this purpose, and
that the range may even be changed while named is running; the new
range is automatically applied when named is reloaded. Explicit
configuration of use-v4-udp-ports and use-v6-udp-ports is encouraged,
so that the ranges are sufficiently large and are reasonably
independent from the ranges used by other applications.
Note
The operational configuration where named runs may prohibit
the use of some ports. For example, Unix systems do not allow
named, if run without root privilege, to use ports less than 1024.
If such ports are included in the specified (or detected) set of query
ports, the corresponding query attempts will fail, resulting in
resolution failures or delay. It is therefore important to configure the
set of ports that can be safely used in the expected operational
environment.
The defaults of the avoid-v4-udp-ports and avoid-v6-udp-ports
options are:
avoid-v4-udp-ports{};avoid-v6-udp-ports{};
Note
BIND 9.5.0 introduced the use-queryport-pool option to support
a pool of such random ports, but this option is now obsolete because
reusing the same ports in the pool may not be sufficiently secure. For
the same reason, it is generally strongly discouraged to specify a
particular port for the query-source or query-source-v6 options;
it implicitly disables the use of randomized port numbers.
use-queryport-pool
This option is obsolete.
queryport-pool-ports
This option is obsolete.
queryport-pool-updateinterval
This option is obsolete.
Note
The address specified in the query-source option is used for both
UDP and TCP queries, but the port applies only to UDP queries. TCP
queries always use a random unprivileged port.
Warning
Specifying a single port is discouraged, as it removes a layer of
protection against spoofing errors.
Warning
The configured port must not be same as the listening port.
Note
See also transfer-source, notify-source and parental-source.
BIND has mechanisms in place to facilitate zone transfers and set limits
on the amount of load that transfers place on the system. The following
options apply to zone transfers.
also-notify
This option defines a global list of IP addresses of name servers that are also
sent NOTIFY messages whenever a fresh copy of the zone is loaded, in
addition to the servers listed in the zone’s NS records. This helps
to ensure that copies of the zones quickly converge on stealth
servers. Optionally, a port may be specified with each
also-notify address to send the notify messages to a port other
than the default of 53. An optional TSIG key can also be specified
with each address to cause the notify messages to be signed; this can
be useful when sending notifies to multiple views. In place of
explicit addresses, one or more named primaries lists can be used.
If an also-notify list is given in a zone statement, it
overrides the optionsalso-notify statement. When a
zonenotify statement is set to no, the IP addresses in the
global also-notify list are not sent NOTIFY messages for that
zone. The default is the empty list (no global notification list).
max-transfer-time-in
Inbound zone transfers running longer than this many minutes are
terminated. The default is 120 minutes (2 hours). The maximum value
is 28 days (40320 minutes).
max-transfer-idle-in
Inbound zone transfers making no progress in this many minutes are
terminated. The default is 60 minutes (1 hour). The maximum value
is 28 days (40320 minutes).
max-transfer-time-out
Outbound zone transfers running longer than this many minutes are
terminated. The default is 120 minutes (2 hours). The maximum value
is 28 days (40320 minutes).
max-transfer-idle-out
Outbound zone transfers making no progress in this many minutes are
terminated. The default is 60 minutes (1 hour). The maximum value
is 28 days (40320 minutes).
notify-rate
This specifies the rate at which NOTIFY requests are sent during normal zone
maintenance operations. (NOTIFY requests due to initial zone loading
are subject to a separate rate limit; see below.) The default is 20
per second. The lowest possible rate is one per second; when set to
zero, it is silently raised to one.
startup-notify-rate
This is the rate at which NOTIFY requests are sent when the name server
is first starting up, or when zones have been newly added to the
name server. The default is 20 per second. The lowest possible rate is
one per second; when set to zero, it is silently raised to one.
serial-query-rate
Secondary servers periodically query primary servers to find out if
zone serial numbers have changed. Each such query uses a minute
amount of the secondary server’s network bandwidth. To limit the amount
of bandwidth used, BIND 9 limits the rate at which queries are sent.
The value of the serial-query-rate option, an integer, is the
maximum number of queries sent per second. The default is 20 per
second. The lowest possible rate is one per second; when set to zero,
it is silently raised to one.
transfer-format
Zone transfers can be sent using two different formats,
one-answer and many-answers. The transfer-format option
is used on the primary server to determine which format it sends.
one-answer uses one DNS message per resource record transferred.
many-answers packs as many resource records as possible into one
message. many-answers is more efficient; the default is many-answers.
transfer-format may be overridden on a per-server basis by using
the server statement.
transfer-message-size
This is an upper bound on the uncompressed size of DNS messages used
in zone transfers over TCP. If a message grows larger than this size,
additional messages are used to complete the zone transfer.
(Note, however, that this is a hint, not a hard limit; if a message
contains a single resource record whose RDATA does not fit within the
size limit, a larger message will be permitted so the record can be
transferred.)
Valid values are between 512 and 65535 octets; any values outside
that range are adjusted to the nearest value within it. The
default is 20480, which was selected to improve message
compression; most DNS messages of this size will compress to less
than 16536 bytes. Larger messages cannot be compressed as
effectively, because 16536 is the largest permissible compression
offset pointer in a DNS message.
This option is mainly intended for server testing; there is rarely
any benefit in setting a value other than the default.
transfers-in
This is the maximum number of inbound zone transfers that can run
concurrently. The default value is 10. Increasing
transfers-in may speed up the convergence of secondary zones, but it
also may increase the load on the local system.
transfers-out
This is the maximum number of outbound zone transfers that can run
concurrently. Zone transfer requests in excess of the limit are
refused. The default value is 10.
transfers-per-ns
This is the maximum number of inbound zone transfers that can concurrently
transfer from a given remote name server. The default value is
2. Increasing transfers-per-ns may speed up the convergence
of secondary zones, but it also may increase the load on the remote name
server. transfers-per-ns may be overridden on a per-server basis
by using the transfers phrase of the server statement.
transfer-source
transfer-source determines which local address is bound to
IPv4 TCP connections used to fetch zones transferred inbound by the
server. It also determines the source IPv4 address, and optionally
the UDP port, used for the refresh queries and forwarded dynamic
updates. If not set, it defaults to a system-controlled value which
is usually the address of the interface “closest to” the remote
end. This address must appear in the remote end’s allow-transfer
option for the zone being transferred, if one is specified. This
statement sets the transfer-source for all zones, but can be
overridden on a per-view or per-zone basis by including a
transfer-source statement within the view or zone block
in the configuration file.
Warning
Specifying a single port is discouraged, as it removes a layer of
protection against spoofing errors.
Warning
The configured port must not be same as the listening port.
transfer-source-v6
This option is the same as transfer-source, except zone transfers are performed
using IPv6.
alt-transfer-source
This indicates an alternate transfer source if the one listed in transfer-source
fails and use-alt-transfer-source is set.
Note
To avoid using the alternate transfer source,
set use-alt-transfer-source appropriately and
do not depend upon getting an answer back to the first refresh
query.
alt-transfer-source-v6
This indicates an alternate transfer source if the one listed in
transfer-source-v6 fails and use-alt-transfer-source is set.
use-alt-transfer-source
This indicates whether the alternate transfer sources should be used. If views are specified,
this defaults to no; otherwise, it defaults to yes.
notify-source
notify-source determines which local source address, and
optionally UDP port, is used to send NOTIFY messages. This
address must appear in the secondary server’s primaries zone clause or
in an allow-notify clause. This statement sets the
notify-source for all zones, but can be overridden on a per-zone
or per-view basis by including a notify-source statement within
the zone or view block in the configuration file.
Warning
Specifying a single port is discouraged, as it removes a layer of
protection against spoofing errors.
Warning
The configured port must not be same as the listening port.
notify-source-v6
This option acts like notify-source, but applies to notify messages sent to IPv6
addresses.
use-v4-udp-ports, avoid-v4-udp-ports, use-v6-udp-ports, and
avoid-v6-udp-ports specify a list of IPv4 and IPv6 UDP ports that
are or are not used as source ports for UDP messages. See
Query Address about how the available ports are
determined. For example, with the following configuration:
UDP ports of IPv6 messages sent from named are in one of the
following ranges: 32768 to 39999, 40001 to 49999, and 60001 to 65535.
avoid-v4-udp-ports and avoid-v6-udp-ports can be used to prevent
named from choosing as its random source port a port that is blocked
by a firewall or a port that is used by other applications; if a
query went out with a source port blocked by a firewall, the answer
would not pass through the firewall and the name server would have to query
again. Note: the desired range can also be represented only with
use-v4-udp-ports and use-v6-udp-ports, and the avoid-
options are redundant in that sense; they are provided for backward
compatibility and to possibly simplify the port specification.
The server’s usage of many system resources can be limited. Scaled
values are allowed when specifying resource limits. For example, 1G
can be used instead of 1073741824 to specify a limit of one
gigabyte. unlimited requests unlimited use, or the maximum available
amount. default uses the limit that was in force when the server was
started. See the description of size_spec in Configuration File Elements.
The following options set operating system resource limits for the name
server process. Some operating systems do not support some or any of the
limits; on such systems, a warning is issued if an unsupported
limit is used.
coresize
This sets the maximum size of a core dump. The default is default.
datasize
This sets the maximum amount of data memory the server may use. The default is
default. This is a hard limit on server memory usage; if the
server attempts to allocate memory in excess of this limit, the
allocation will fail, which may in turn leave the server unable to
perform DNS service. Therefore, this option is rarely useful as a way
to limit the amount of memory used by the server, but it can be
used to raise an operating system data size limit that is too small
by default. To limit the amount of memory used by the
server, use the max-cache-size and recursive-clients options
instead.
files
This sets the maximum number of files the server may have open concurrently.
The default is unlimited.
stacksize
This sets the maximum amount of stack memory the server may use. The default is
default.
The following options set limits on the server’s resource consumption
that are enforced internally by the server rather than by the operating
system.
max-journal-size
This sets a maximum size for each journal file (see The Journal File),
expressed in bytes or, if followed by an
optional unit suffix (‘k’, ‘m’, or ‘g’), in kilobytes, megabytes, or
gigabytes. When the journal file approaches the specified size, some
of the oldest transactions in the journal are automatically
removed. The largest permitted value is 2 gigabytes. Very small
values are rounded up to 4096 bytes. It is possible to specify unlimited,
which also means 2 gigabytes. If the limit is set to default or
left unset, the journal is allowed to grow up to twice as large
as the zone. (There is little benefit in storing larger journals.)
This option may also be set on a per-zone basis.
max-records
This sets the maximum number of records permitted in a zone. The default is
zero, which means the maximum is unlimited.
recursive-clients
This sets the maximum number (a “hard quota”) of simultaneous recursive lookups
the server performs on behalf of clients. The default is
1000. Because each recursing client uses a fair bit of memory (on
the order of 20 kilobytes), the value of the recursive-clients
option may have to be decreased on hosts with limited memory.
recursive-clients defines a “hard quota” limit for pending
recursive clients; when more clients than this are pending, new
incoming requests are not accepted, and for each incoming request
a previous pending request is dropped.
A “soft quota” is also set. When this lower quota is exceeded,
incoming requests are accepted, but for each one, a pending request
is dropped. If recursive-clients is greater than 1000, the
soft quota is set to recursive-clients minus 100; otherwise it is
set to 90% of recursive-clients.
tcp-clients
This is the maximum number of simultaneous client TCP connections that the
server accepts. The default is 150.
clients-per-query; max-clients-per-query
These set the initial value (minimum) and maximum number of recursive
simultaneous clients for any given query (<qname,qtype,qclass>) that
the server accepts before dropping additional clients. named
attempts to self-tune this value and changes are logged. The
default values are 10 and 100.
This value should reflect how many queries come in for a given name
in the time it takes to resolve that name. If the number of queries
exceeds this value, named assumes that it is dealing with a
non-responsive zone and drops additional queries. If it gets a
response after dropping queries, it raises the estimate. The
estimate is then lowered in 20 minutes if it has remained
unchanged.
If clients-per-query is set to zero, there is no limit on
the number of clients per query and no queries are dropped.
If max-clients-per-query is set to zero, there is no upper
bound other than that imposed by recursive-clients.
fetches-per-zone
This sets the maximum number of simultaneous iterative queries to any one
domain that the server permits before blocking new queries for
data in or beneath that zone. This value should reflect how many
fetches would normally be sent to any one zone in the time it would
take to resolve them. It should be smaller than
recursive-clients.
When many clients simultaneously query for the same name and type,
the clients are all attached to the same fetch, up to the
max-clients-per-query limit, and only one iterative query is
sent. However, when clients are simultaneously querying for
different names or types, multiple queries are sent and
max-clients-per-query is not effective as a limit.
Optionally, this value may be followed by the keyword drop or
fail, indicating whether queries which exceed the fetch quota for
a zone are dropped with no response, or answered with SERVFAIL.
The default is drop.
If fetches-per-zone is set to zero, there is no limit on the
number of fetches per query and no queries are dropped. The
default is zero.
The current list of active fetches can be dumped by running
rndcrecursing. The list includes the number of active fetches
for each domain and the number of queries that have been passed
(allowed) or dropped (spilled) as a result of the fetches-per-zone
limit. (Note: these counters are not cumulative over time;
whenever the number of active fetches for a domain drops to zero,
the counter for that domain is deleted, and the next time a fetch
is sent to that domain, it is recreated with the counters set
to zero.)
fetches-per-server
This sets the maximum number of simultaneous iterative queries that the server
allows to be sent to a single upstream name server before
blocking additional queries. This value should reflect how many
fetches would normally be sent to any one server in the time it would
take to resolve them. It should be smaller than
recursive-clients.
Optionally, this value may be followed by the keyword drop or
fail, indicating whether queries are dropped with no
response or answered with SERVFAIL, when all of the servers
authoritative for a zone are found to have exceeded the per-server
quota. The default is fail.
If fetches-per-server is set to zero, there is no limit on
the number of fetches per query and no queries are dropped. The
default is zero.
The fetches-per-server quota is dynamically adjusted in response
to detected congestion. As queries are sent to a server and either are
answered or time out, an exponentially weighted moving average
is calculated of the ratio of timeouts to responses. If the current
average timeout ratio rises above a “high” threshold, then
fetches-per-server is reduced for that server. If the timeout
ratio drops below a “low” threshold, then fetches-per-server is
increased. The fetch-quota-params options can be used to adjust
the parameters for this calculation.
fetch-quota-params
This sets the parameters to use for dynamic resizing of the
fetches-per-server quota in response to detected congestion.
The first argument is an integer value indicating how frequently to
recalculate the moving average of the ratio of timeouts to responses
for each server. The default is 100, meaning that BIND recalculates the
average ratio after every 100 queries have either been answered or
timed out.
The remaining three arguments represent the “low” threshold
(defaulting to a timeout ratio of 0.1), the “high” threshold
(defaulting to a timeout ratio of 0.3), and the discount rate for the
moving average (defaulting to 0.7). A higher discount rate causes
recent events to weigh more heavily when calculating the moving
average; a lower discount rate causes past events to weigh more
heavily, smoothing out short-term blips in the timeout ratio. These
arguments are all fixed-point numbers with precision of 1/100; at
most two places after the decimal point are significant.
reserved-sockets
This sets the number of file descriptors reserved for TCP, stdio, etc. This
needs to be big enough to cover the number of interfaces named
listens on plus tcp-clients, as well as to provide room for
outgoing TCP queries and incoming zone transfers. The default is
512. The minimum value is 128 and the maximum value is
128 fewer than maxsockets (-S). This option may be removed in the
future.
This option has little effect on Windows.
max-cache-size
This sets the maximum amount of memory to use for an individual cache
database and its associated metadata, in bytes or percentage of total
physical memory. By default, each view has its own separate cache,
which means the total amount of memory required for cache data is the
sum of the cache database sizes for all views (unless the
attach-cache option is used).
When the amount of data in a cache database reaches the configured
limit, named starts purging non-expired records (following an
LRU-based strategy).
The default size limit for each individual cache is:
90% of physical memory for views with recursion set to
yes (the default), or
2 MB for views with recursion set to no.
Any positive value smaller than 2 MB is ignored and reset to 2 MB.
The keyword unlimited, or the value 0, places no limit on the
cache size; records are then purged from the cache only when they
expire (according to their TTLs).
Note
For configurations which define multiple views with separate
caches and recursion enabled, it is recommended to set
max-cache-size appropriately for each view, as using the
default value of that option (90% of physical memory for each
individual cache) may lead to memory exhaustion over time.
Upon startup and reconfiguration, caches with a limited size
preallocate a small amount of memory (less than 1% of
max-cache-size for a given view). This preallocation serves as an
optimization to eliminate extra latency introduced by resizing
internal cache structures.
On systems where detection of the amount of physical memory is not
supported, percentage-based values fall back to unlimited. Note
that the amount of physical memory available is only detected on
startup, so named does not adjust the cache size limits if the
amount of physical memory is changed at runtime.
tcp-listen-queue
This sets the listen-queue depth. The default and minimum is 10. If the kernel
supports the accept filter “dataready”, this also controls how many
TCP connections are queued in kernel space waiting for some
data before being passed to accept. Non-zero values less than 10 are
silently raised. A value of 0 may also be used; on most platforms
this sets the listen-queue length to a system-defined default value.
tcp-initial-timeout
This sets the amount of time (in units of 100 milliseconds) that the server waits on
a new TCP connection for the first message from the client. The
default is 300 (30 seconds), the minimum is 25 (2.5 seconds), and the
maximum is 1200 (two minutes). Values above the maximum or below the
minimum are adjusted with a logged warning. (Note: this value
must be greater than the expected round-trip delay time; otherwise, no
client will ever have enough time to submit a message.) This value
can be updated at runtime by using rndctcp-timeouts.
tcp-idle-timeout
This sets the amount of time (in units of 100 milliseconds) that the server waits on
an idle TCP connection before closing it, when the client is not using
the EDNS TCP keepalive option. The default is 300 (30 seconds), the
maximum is 1200 (two minutes), and the minimum is 1 (one-tenth of a
second). Values above the maximum or below the minimum are
adjusted with a logged warning. See tcp-keepalive-timeout for
clients using the EDNS TCP keepalive option. This value can be
updated at runtime by using rndctcp-timeouts.
tcp-keepalive-timeout
This sets the amount of time (in units of 100 milliseconds) that the server waits on
an idle TCP connection before closing it, when the client is using the
EDNS TCP keepalive option. The default is 300 (30 seconds), the
maximum is 65535 (about 1.8 hours), and the minimum is 1 (one-tenth
of a second). Values above the maximum or below the minimum are
adjusted with a logged warning. This value may be greater than
tcp-idle-timeout because clients using the EDNS TCP keepalive
option are expected to use TCP connections for more than one message.
This value can be updated at runtime by using rndctcp-timeouts.
tcp-advertised-timeout
This sets the timeout value (in units of 100 milliseconds) that the server sends
in responses containing the EDNS TCP keepalive option, which informs a
client of the amount of time it may keep the session open. The
default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours),
and the minimum is 0, which signals that the clients must close TCP
connections immediately. Ordinarily this should be set to the same
value as tcp-keepalive-timeout. This value can be updated at
runtime by using rndctcp-timeouts.
update-quota
This is the maximum number of simultaneous DNS UPDATE messages that
the server will accept for updating local authoritiative zones or
forwarding to a primary server. The default is 100.
The server performs zone maintenance tasks for all zones marked
as dialup whenever this interval expires. The default is 60
minutes. Reasonable values are up to 1 day (1440 minutes). The
maximum value is 28 days (40320 minutes). If set to 0, no zone
maintenance for these zones occurs.
interface-interval
The server scans the network interface list every interface-interval
minutes. The default is 60 minutes; the maximum value is 28 days (40320
minutes). If set to 0, interface scanning only occurs when the configuration
file is loaded, or when automatic-interface-scan is enabled and supported
by the operating system. After the scan, the server begins listening for
queries on any newly discovered interfaces (provided they are allowed by the
listen-on configuration), and stops listening on interfaces that have
gone away. For convenience, TTL-style time-unit suffixes may be used to
specify the value. It also accepts ISO 8601 duration formats.
The response to a DNS query may consist of multiple resource records
(RRs) forming a resource record set (RRset). The name server
normally returns the RRs within the RRset in an indeterminate order (but
see the rrset-order statement in RRset Ordering). The client resolver code should
rearrange the RRs as appropriate: that is, using any addresses on the
local net in preference to other addresses. However, not all resolvers
can do this or are correctly configured. When a client is using a local
server, the sorting can be performed in the server, based on the
client’s address. This only requires configuring the name servers, not
all the clients.
The sortlist statement (see below) takes an address_match_list and
interprets it in a special way. Each top-level statement in the sortlist
must itself be an explicit address_match_list with one or two elements. The
first element (which may be an IP address, an IP prefix, an ACL name, or a nested
address_match_list) of each top-level list is checked against the source
address of the query until a match is found. When the addresses in the first
element overlap, the first rule to match is selected.
Once the source address of the query has been matched, if the top-level
statement contains only one element, the actual primitive element that
matched the source address is used to select the address in the response
to move to the beginning of the response. If the statement is a list of
two elements, then the second element is interpreted as a topology
preference list. Each top-level element is assigned a distance, and the
address in the response with the minimum distance is moved to the
beginning of the response.
In the following example, any queries received from any of the addresses
of the host itself get responses preferring addresses on any of the
locally connected networks. Next most preferred are addresses on the
192.168.1/24 network, and after that either the 192.168.2/24 or
192.168.3/24 network, with no preference shown between these two
networks. Queries received from a host on the 192.168.1/24 network
prefer other addresses on that network to the 192.168.2/24 and
192.168.3/24 networks. Queries received from a host on the 192.168.4/24
or the 192.168.5/24 network only prefer other addresses on their
directly connected networks.
The following example illlustrates reasonable behavior for the local host
and hosts on directly connected networks. Responses sent to queries from the
local host favor any of the directly connected networks. Responses
sent to queries from any other hosts on a directly connected network
prefer addresses on that same network. Responses to other queries
are not sorted.
While alternating the order of records in a DNS response between
subsequent queries is a known load distribution technique, certain
caveats apply (mostly stemming from caching) which usually make it a
suboptimal choice for load balancing purposes when used on its own.
The rrset-order statement permits configuration of the ordering of
the records in a multiple-record response. See also:
The sortlist Statement.
Each rule in an rrset-order statement is defined as follows:
[class <class_name>] [type <type_name>] [name "<domain_name>"] order <ordering>
The default qualifiers for each rule are:
If no class is specified, the default is ANY.
If no type is specified, the default is ANY.
If no name is specified, the default is * (asterisk).
<domain_name> only matches the name itself, not any of its
subdomains. To make a rule match all subdomains of a given name, a
wildcard name (*.<domain_name>) must be used. Note that
*.<domain_name> does not match <domain_name> itself; to
specify RRset ordering for a name and all of its subdomains, two
separate rules must be defined: one for <domain_name> and one for
*.<domain_name>.
The legal values for <ordering> are:
fixed
Records are returned in the order they are defined in the zone file.
Note
The fixed option is only available if BIND is configured with
--enable-fixed-rrset at compile time.
random
Records are returned in a random order.
cyclic
Records are returned in a cyclic round-robin order, rotating by one
record per query.
none
Records are returned in the order they were retrieved from the
database. This order is indeterminate, but remains consistent as
long as the database is not modified.
The default RRset order used depends on whether any rrset-order
statements are present in the configuration file used by named:
If no rrset-order statement is present in the configuration
file, the implicit default is to return all records in random
order.
If any rrset-order statements are present in the configuration
file, but no ordering rule specified in these statements matches a
given RRset, the default order for that RRset is none.
Note that if multiple rrset-order statements are present in the
configuration file (at both the options and view levels), they
are not combined; instead, the more-specific one (view) replaces
the less-specific one (options).
If multiple rules within a single rrset-order statement match a
given RRset, the first matching rule is applied.
This sets the number of seconds to cache a SERVFAIL response due to DNSSEC
validation failure or other general server failure. If set to 0,
SERVFAIL caching is disabled. The SERVFAIL cache is not consulted if
a query has the CD (Checking Disabled) bit set; this allows a query
that failed due to DNSSEC validation to be retried without waiting
for the SERVFAIL TTL to expire.
The maximum value is 30 seconds; any higher value is
silently reduced. The default is 1 second.
min-ncache-ttl
To reduce network traffic and increase performance, the server stores
negative answers. min-ncache-ttl is used to set a minimum
retention time for these answers in the server, in seconds. For
convenience, TTL-style time-unit suffixes may be used to specify the
value. It also accepts ISO 8601 duration formats.
The default min-ncache-ttl is 0 seconds. min-ncache-ttl cannot
exceed 90 seconds and is truncated to 90 seconds if set to a greater
value.
min-cache-ttl
This sets the minimum time for which the server caches ordinary (positive)
answers, in seconds. For convenience, TTL-style time-unit suffixes may be used
to specify the value. It also accepts ISO 8601 duration formats.
The default min-cache-ttl is 0 seconds. min-cache-ttl cannot
exceed 90 seconds and is truncated to 90 seconds if set to a greater
value.
max-ncache-ttl
To reduce network traffic and increase performance, the server stores
negative answers. max-ncache-ttl is used to set a maximum retention time
for these answers in the server, in seconds. For convenience, TTL-style
time-unit suffixes may be used to specify the value. It also accepts ISO 8601
duration formats.
The default max-ncache-ttl is 10800 seconds (3 hours). max-ncache-ttl
cannot exceed 7 days and is silently truncated to 7 days if set to a
greater value.
max-cache-ttl
This sets the maximum time for which the server caches ordinary (positive)
answers, in seconds. For convenience, TTL-style time-unit suffixes may be used
to specify the value. It also accepts ISO 8601 duration formats.
The default max-cache-ttl is 604800 (one week). A value of zero may cause
all queries to return SERVFAIL, because of lost caches of intermediate RRsets
(such as NS and glue AAAA/A records) in the resolution process.
max-stale-ttl
If retaining stale RRsets in cache is enabled, and returning of stale cached
answers is also enabled, max-stale-ttl sets the maximum time for which
the server retains records past their normal expiry to return them as stale
records, when the servers for those records are not reachable. The default
is 1 day. The minimum allowed is 1 second; a value of 0 is updated silently
to 1 second.
For stale answers to be returned, the retaining of them in cache must be
enabled via the configuration option stale-cache-enable, and returning
cached answers must be enabled, either in the configuration file using the
stale-answer-enable option or by calling rndcserve-staleon.
When stale-cache-enable is set to no, setting the max-stale-ttl
has no effect, the value of max-cache-ttl will be 0 in such case.
resolver-nonbackoff-tries
This specifies how many retries occur before exponential backoff kicks in. The
default is 3.
resolver-retry-interval
This sets the base retry interval in milliseconds. The default is 800.
sig-validity-interval
this specifies the upper bound of the number of days that RRSIGs
generated by named are valid; the default is 30 days,
with a maximum of 3660 days (10 years). The optional second value
specifies the minimum bound on those RRSIGs and also determines
how long before expiry named starts regenerating those RRSIGs.
The default value for the lower bound is 1/4 of the upper bound;
it is expressed in days if the upper bound is greater than 7,
and hours if it is less than or equal to 7 days.
When new RRSIGs are generated, the length of time is randomly
chosen between these two limits, to spread out the re-signing
load. When RRSIGs are re-generated, the upper bound is used, with
a small amount of jitter added. New RRSIGs are generated by a
number of processes, including the processing of UPDATE requests
(ref:dynamic_update), the addition and removal of records via
in-line signing, and the initial signing of a zone.
The signature inception time is unconditionally set to one hour
before the current time, to allow for a limited amount of clock skew.
The sig-validity-interval can be overridden for DNSKEY records by
setting dnskey-sig-validity.
The sig-validity-interval should be at least several multiples
of the SOA expire interval, to allow for reasonable interaction
between the various timer and expiry dates.
dnskey-sig-validity
This specifies the number of days into the future when DNSSEC signatures
that are automatically generated for DNSKEY RRsets as a result of
dynamic updates (Dynamic Update) will expire.
If set to a non-zero value, this overrides the value set by
sig-validity-interval. The default is zero, meaning
sig-validity-interval is used. The maximum value is 3660 days (10
years), and higher values are rejected.
sig-signing-nodes
This specifies the maximum number of nodes to be examined in each quantum,
when signing a zone with a new DNSKEY. The default is 100.
sig-signing-signatures
This specifies a threshold number of signatures that terminates
processing a quantum, when signing a zone with a new DNSKEY. The
default is 10.
sig-signing-type
This specifies a private RDATA type to be used when generating signing-state
records. The default is 65534.
This parameter may be removed in a future version,
once there is a standard type.
Signing-state records are used internally by named to track
the current state of a zone-signing process, i.e., whether it is
still active or has been completed. The records can be inspected
using the command rndcsigning-listzone. Once named has
finished signing a zone with a particular key, the signing-state
record associated with that key can be removed from the zone by
running rndcsigning-clearkeyid/algorithmzone. To clear all of
the completed signing-state records for a zone, use
rndcsigning-clearallzone.
These options control the server’s behavior on refreshing a zone
(querying for SOA changes) or retrying failed transfers. Usually the
SOA values for the zone are used, up to a hard-coded maximum expiry
of 24 weeks. However, these values are set by the primary, giving
secondary server administrators little control over their contents.
These options allow the administrator to set a minimum and maximum
refresh and retry time in seconds per-zone, per-view, or globally.
These options are valid for secondary and stub zones, and clamp the SOA
refresh and retry times to the specified values.
The following defaults apply: min-refresh-time 300 seconds,
max-refresh-time 2419200 seconds (4 weeks), min-retry-time
500 seconds, and max-retry-time 1209600 seconds (2 weeks).
edns-udp-size
This sets the maximum advertised EDNS UDP buffer size, in bytes, to control
the size of packets received from authoritative servers in response
to recursive queries. Valid values are 512 to 4096; values outside
this range are silently adjusted to the nearest value within it.
The default value is 1232.
The usual reason for setting edns-udp-size to a non-default value
is to get UDP answers to pass through broken firewalls that block
fragmented packets and/or block UDP DNS packets that are greater than
512 bytes.
When named first queries a remote server, it advertises a UDP
buffer size of 512, as this has the greatest chance of success on the
first try.
If the initial query is successful with EDNS advertising a buffer size of
512, then named will advertise progressively larger buffer sizes on
successive queries, until responses begin timing out or edns-udp-size is
reached.
The default buffer sizes used by named are 512, 1232, 1432, and
4096, but never exceeding edns-udp-size. (The values 1232 and
1432 are chosen to allow for an IPv4-/IPv6-encapsulated UDP message
to be sent without fragmentation at the minimum MTU sizes for
Ethernet and IPv6 networks.)
The named now sets the DON’T FRAGMENT flag on outgoing UDP packets.
According to the measurements done by multiple parties this should not be
causing any operational problems as most of the Internet “core” is able to
cope with IP message sizes between 1400-1500 bytes, the 1232 size was picked
as a conservative minimal number that could be changed by the DNS operator to
a estimated path MTU minus the estimated header space. In practice, the
smallest MTU witnessed in the operational DNS community is 1500 octets, the
Ethernet maximum payload size, so a a useful default for maximum DNS/UDP
payload size on reliable networks would be 1432.
Any server-specific edns-udp-size setting has precedence over all
the above rules.
max-udp-size
This sets the maximum EDNS UDP message size that named sends, in bytes.
Valid values are 512 to 4096; values outside this range are
silently adjusted to the nearest value within it. The default value
is 1232.
This value applies to responses sent by a server; to set the
advertised buffer size in queries, see edns-udp-size.
The usual reason for setting max-udp-size to a non-default value
is to allow UDP answers to pass through broken firewalls that block
fragmented packets and/or block UDP packets that are greater than 512
bytes. This is independent of the advertised receive buffer
(edns-udp-size).
Setting this to a low value encourages additional TCP traffic to
the name server.
masterfile-format
This specifies the file format of zone files (see Additional File Formats
for details). The default value is text, which is the standard
textual representation, except for secondary zones, in which the default
value is raw. Files in formats other than text are typically
expected to be generated by the named-compilezone tool, or dumped by
named.
Note that when a zone file in a format other than text is loaded,
named may omit some of the checks which are performed for a file in
text format. For example, check-names only applies when loading
zones in text format, and max-zone-ttl only applies to text
and raw. Zone files in binary formats should be generated with the
same check level as that specified in the named configuration file.
map format files are loaded directly into memory via memory mapping,
with only minimal validity checking. Because they are not guaranteed to
be compatible from one version of BIND 9 to another, and are not
compatible from one system architecture to another, they should be used
with caution. See Additional File Formats for further discussion.
When configured in options, this statement sets the
masterfile-format for all zones, but it can be overridden on a
per-zone or per-view basis by including a masterfile-format
statement within the zone or view block in the configuration
file.
masterfile-style
This specifies the formatting of zone files during dump, when the
masterfile-format is text. This option is ignored with any
other masterfile-format.
When set to relative, records are printed in a multi-line format,
with owner names expressed relative to a shared origin. When set to
full, records are printed in a single-line format with absolute
owner names. The full format is most suitable when a zone file
needs to be processed automatically by a script. The relative
format is more human-readable, and is thus suitable when a zone is to
be edited by hand. The default is relative.
max-recursion-depth
This sets the maximum number of levels of recursion that are permitted at
any one time while servicing a recursive query. Resolving a name may
require looking up a name server address, which in turn requires
resolving another name, etc.; if the number of recursions exceeds
this value, the recursive query is terminated and returns SERVFAIL.
The default is 7.
max-recursion-queries
This sets the maximum number of iterative queries that may be sent while
servicing a recursive query. If more queries are sent, the recursive
query is terminated and returns SERVFAIL. The default is 100.
notify-delay
This sets the delay, in seconds, between sending sets of NOTIFY messages
for a zone. Whenever a NOTIFY message is sent for a zone, a timer will
be set for this duration. If the zone is updated again before the timer
expires, the NOTIFY for that update will be postponed. The default is 5
seconds.
The overall rate at which NOTIFY messages are sent for all zones is
controlled by notify-rate.
max-rsa-exponent-size
This sets the maximum RSA exponent size, in bits, that is accepted when
validating. Valid values are 35 to 4096 bits. The default, zero, is
also accepted and is equivalent to 4096.
prefetch
When a query is received for cached data which is to expire shortly,
named can refresh the data from the authoritative server
immediately, ensuring that the cache always has an answer available.
prefetch specifies the “trigger” TTL value at which prefetch
of the current query takes place; when a cache record with a
lower or equal TTL value is encountered during query processing, it is
refreshed. Valid trigger TTL values are 1 to 10 seconds. Values
larger than 10 seconds are silently reduced to 10. Setting a
trigger TTL to zero causes prefetch to be disabled. The default
trigger TTL is 2.
An optional second argument specifies the “eligibility” TTL: the
smallest original TTL value that is accepted for a record to
be eligible for prefetching. The eligibility TTL must be at least six
seconds longer than the trigger TTL; if not, named
silently adjusts it upward. The default eligibility TTL is 9.
v6-bias
When determining the next name server to try, this indicates by how many
milliseconds to prefer IPv6 name servers. The default is 50
milliseconds.
The server provides some helpful diagnostic information through a number
of built-in zones under the pseudo-top-level-domain bind in the
CHAOS class. These zones are part of a built-in view
(see view Statement Grammar) of class CHAOS, which is
separate from the default view of class IN. Most global
configuration options (allow-query, etc.) apply to this view,
but some are locally overridden: notify, recursion, and
allow-new-zones are always set to no, and rate-limit is set
to allow three responses per second.
To disable these zones, use the options below or hide the
built-in CHAOS view by defining an explicit view of class CHAOS
that matches all clients.
version
This is the version the server should report via a query of the name
version.bind with type TXT and class CHAOS. The default is
the real version number of this server. Specifying versionnone
disables processing of the queries.
Setting version to any value (including none) also disables
queries for authors.bindTXTCH.
hostname
This is the hostname the server should report via a query of the name
hostname.bind with type TXT and class CHAOS. This defaults
to the hostname of the machine hosting the name server, as found by
the gethostname() function. The primary purpose of such queries is to
identify which of a group of anycast servers is actually answering
the queries. Specifying hostnamenone; disables processing of
the queries.
server-id
This is the ID the server should report when receiving a Name Server
Identifier (NSID) query, or a query of the name ID.SERVER with
type TXT and class CHAOS. The primary purpose of such queries is
to identify which of a group of anycast servers is actually answering
the queries. Specifying server-idnone; disables processing of
the queries. Specifying server-idhostname; causes named
to use the hostname as found by the gethostname() function. The
default server-id is none.
The named server has some built-in empty zones, for SOA and NS records
only. These are for zones that should normally be answered locally and for
which queries should not be sent to the Internet’s root servers. The
official servers that cover these namespaces return NXDOMAIN responses
to these queries. In particular, these cover the reverse namespaces for
addresses from RFC 1918, RFC 4193, RFC 5737, and RFC 6598. They also
include the reverse namespace for the IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address, and the IPv6
unknown address.
The server attempts to determine if a built-in zone already exists
or is active (covered by a forward-only forwarding declaration) and does
not create an empty zone if either is true.
Empty zones can be set at the view level and only apply to views of
class IN. Disabled empty zones are only inherited from options if there
are no disabled empty zones specified at the view level. To override the
options list of disabled zones, disable the root zone at the
view level. For example:
disable-empty-zone".";
If using the address ranges covered here,
reverse zones covering the addresses should already be in place. In practice this
appears to not be the case, with many queries being made to the
infrastructure servers for names in these spaces. So many, in fact, that
sacrificial servers had to be deployed to channel the query load
away from the infrastructure servers.
Note
The real parent servers for these zones should disable all empty zones
under the parent zone they serve. For the real root servers, this is
all built-in empty zones. This enables them to return referrals
to deeper in the tree.
empty-server
This specifies the server name that appears in the returned SOA record for
empty zones. If none is specified, the zone’s name is used.
empty-contact
This specifies the contact name that appears in the returned SOA record for
empty zones. If none is specified, “.” is used.
empty-zones-enable
This enables or disables all empty zones. By default, they are enabled.
disable-empty-zone
This disables individual empty zones. By default, none are disabled. This
option can be specified multiple times.
BIND 9 provides the ability to filter out responses from external
DNS servers containing certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if the
corresponding IPv4 or IPv6 addresses match the given
address_match_list of the deny-answer-addresses option. It can
also reject CNAME or DNAME records if the “alias” name (i.e., the CNAME
alias or the substituted query name due to DNAME) matches the given
namelist of the deny-answer-aliases option, where “match” means
the alias name is a subdomain of one of the name_list elements. If
the optional namelist is specified with except-from, records
whose query name matches the list are accepted regardless of the
filter setting. Likewise, if the alias name is a subdomain of the
corresponding zone, the deny-answer-aliases filter does not apply;
for example, even if “example.com” is specified for
deny-answer-aliases,
www.example.com.CNAMExxx.example.com.
returned by an “example.com” server is accepted.
In the address_match_list of the deny-answer-addresses option,
only ip_addr and ip_prefix are meaningful; any key_id is
silently ignored.
If a response message is rejected due to the filtering, the entire
message is discarded without being cached, and a SERVFAIL error is
returned to the client.
This filtering is intended to prevent “DNS rebinding attacks,” in which
an attacker, in response to a query for a domain name the attacker
controls, returns an IP address within the user’s own network or an alias name
within the user’s own domain. A naive web browser or script could then serve
as an unintended proxy, allowing the attacker to get access to an
internal node of the local network that could not be externally accessed
otherwise. See the paper available at
https://dl.acm.org/doi/10.1145/1315245.1315298 for more details
about these attacks.
For example, with a domain named “example.net” and an internal
network using an IPv4 prefix 192.0.2.0/24, an administrator might specify the
following rules:
If an external attacker let a web browser in the local network look up
an IPv4 address of “attacker.example.com”, the attacker’s DNS server
would return a response like this:
attacker.example.com.A192.0.2.1
in the answer section. Since the rdata of this record (the IPv4 address)
matches the specified prefix 192.0.2.0/24, this response would be
ignored.
On the other hand, if the browser looked up a legitimate internal web
server “www.example.net” and the following response were returned to the
BIND 9 server:
www.example.net.A192.0.2.2
it would be accepted, since the owner name “www.example.net” matches the
except-from element, “example.net”.
Note that this is not really an attack on the DNS per se. In fact, there
is nothing wrong with having an “external” name mapped to an “internal”
IP address or domain name from the DNS point of view; it might actually
be provided for a legitimate purpose, such as for debugging. As long as
the mapping is provided by the correct owner, it either is not possible or does
not make sense to detect whether the intent of the mapping is legitimate
within the DNS. The “rebinding” attack must primarily be
protected at the application that uses the DNS. For a large site,
however, it may be difficult to protect all possible applications at
once. This filtering feature is provided only to help such an
operational environment; turning it on is generally discouraged
unless there is no other choice and the attack is a
real threat to applications.
Care should be particularly taken if using this option for
addresses within 127.0.0.0/8. These addresses are obviously “internal,”
but many applications conventionally rely on a DNS mapping from some
name to such an address. Filtering out DNS records containing this
address spuriously can break such applications.
BIND 9 includes a limited mechanism to modify DNS responses for requests
analogous to email anti-spam DNS rejection lists. Responses can be changed to
deny the existence of domains (NXDOMAIN), deny the existence of IP
addresses for domains (NODATA), or contain other IP addresses or data.
Response policy zones are named in the response-policy option for
the view, or among the global options if there is no response-policy
option for the view. Response policy zones are ordinary DNS zones
containing RRsets that can be queried normally if allowed. It is usually
best to restrict those queries with something like
allow-query{localhost;};. Note that zones using
masterfile-formatmap cannot be used as policy zones.
A response-policy option can support multiple policy zones. To
maximize performance, a radix tree is used to quickly identify response
policy zones containing triggers that match the current query. This
imposes an upper limit of 64 on the number of policy zones in a single
response-policy option; more than that is a configuration error.
Rules encoded in response policy zones are processed after those defined in
Access Control. All queries from clients which are not permitted access
to the resolver are answered with a status code of REFUSED, regardless of
configured RPZ rules.
Five policy triggers can be encoded in RPZ records.
RPZ-CLIENT-IP
IP records are triggered by the IP address of the DNS client. Client
IP address triggers are encoded in records that have owner names that
are subdomains of rpz-client-ip, relativized to the policy zone
origin name, and that encode an address or address block. IPv4 addresses
are represented as prefixlength.B4.B3.B2.B1.rpz-client-ip. The
IPv4 prefix length must be between 1 and 32. All four bytes - B4, B3,
B2, and B1 - must be present. B4 is the decimal value of the least
significant byte of the IPv4 address as in IN-ADDR.ARPA.
IPv6 addresses are encoded in a format similar to the standard IPv6
text representation,
prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip. Each of
W8,…,W1 is a one- to four-digit hexadecimal number representing 16
bits of the IPv6 address as in the standard text representation of
IPv6 addresses, but reversed as in IP6.ARPA. (Note that this
representation of IPv6 addresses is different from IP6.ARPA, where each
hex digit occupies a label.) All 8 words must be present except when
one set of consecutive zero words is replaced with .zz., analogous
to double colons (::) in standard IPv6 text encodings. The IPv6
prefix length must be between 1 and 128.
QNAME
QNAME policy records are triggered by query names of requests and
targets of CNAME records resolved to generate the response. The owner
name of a QNAME policy record is the query name relativized to the
policy zone.
RPZ-IP
IP triggers are IP addresses in an A or AAAA record in the ANSWER
section of a response. They are encoded like client-IP triggers,
except as subdomains of rpz-ip.
RPZ-NSDNAME
NSDNAME triggers match names of authoritative servers for the query name, a
parent of the query name, a CNAME for the query name, or a parent of a CNAME.
They are encoded as subdomains of rpz-nsdname, relativized
to the RPZ origin name. NSIP triggers match IP addresses in A and AAAA
RRsets for domains that can be checked against NSDNAME policy records. The
nsdname-enable phrase turns NSDNAME triggers off or on for a single
policy zone or for all zones.
If authoritative name servers for the query name are not yet known, named
recursively looks up the authoritative servers for the query name before
applying an RPZ-NSDNAME rule, which can cause a processing delay.
RPZ-NSIP
NSIP triggers match the IP addresses of authoritative servers. They
are encoded like IP triggers, except as subdomains of rpz-nsip.
NSDNAME and NSIP triggers are checked only for names with at least
min-ns-dots dots. The default value of min-ns-dots is 1, to
exclude top-level domains. The nsip-enable phrase turns NSIP
triggers off or on for a single policy zone or for all zones.
If a name server’s IP address is not yet known, named
recursively looks up the IP address before applying an RPZ-NSIP rule,
which can cause a processing delay. To speed up processing at the cost
of precision, the nsip-wait-recurse option can be used; when set
to no, RPZ-NSIP rules are only applied when a name server’s
IP address has already been looked up and cached. If a server’s IP
address is not in the cache, the RPZ-NSIP rule is ignored,
but the address is looked up in the background and the rule
is applied to subsequent queries. The default is yes,
meaning RPZ-NSIP rules are always applied, even if an address
needs to be looked up first.
The query response is checked against all response policy zones, so two
or more policy records can be triggered by a response. Because DNS
responses are rewritten according to at most one policy record, a single
record encoding an action (other than DISABLED actions) must be
chosen. Triggers, or the records that encode them, are chosen for
rewriting in the following order:
Choose the triggered record in the zone that appears first in the
response-policy option.
Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP triggers in a
single zone.
Among NSDNAME triggers, prefer the trigger that matches the smallest
name under the DNSSEC ordering.
Among IP or NSIP triggers, prefer the trigger with the longest
prefix.
Among triggers with the same prefix length, prefer the IP or NSIP
trigger that matches the smallest IP address.
When the processing of a response is restarted to resolve DNAME or CNAME
records and a policy record set has not been triggered, all response
policy zones are again consulted for the DNAME or CNAME names and
addresses.
RPZ record sets are any types of DNS record, except DNAME or DNSSEC, that
encode actions or responses to individual queries. Any of the policies
can be used with any of the triggers. For example, while the
TCP-only policy is commonly used with client-IP triggers, it can
be used with any type of trigger to force the use of TCP for responses
with owner names in a zone.
PASSTHRU
The auto-acceptance policy is specified by a CNAME whose target is
rpz-passthru. It causes the response to not be rewritten and is
most often used to “poke holes” in policies for CIDR blocks.
DROP
The auto-rejection policy is specified by a CNAME whose target is
rpz-drop. It causes the response to be discarded. Nothing is sent
to the DNS client.
TCP-Only
The “slip” policy is specified by a CNAME whose target is
rpz-tcp-only. It changes UDP responses to short, truncated DNS
responses that require the DNS client to try again with TCP. It is
used to mitigate distributed DNS reflection attacks.
NXDOMAIN
The “domain undefined” response is encoded by a CNAME whose target is
the root domain (.).
NODATA
The empty set of resource records is specified by a CNAME whose target
is the wildcard top-level domain (*.). It rewrites the response to
NODATA or ANCOUNT=0.
LocalData
A set of ordinary DNS records can be used to answer queries. Queries
for record types not in the set are answered with NODATA.
A special form of local data is a CNAME whose target is a wildcard
such as *.example.com. It is used as if an ordinary CNAME after
the asterisk (*) has been replaced with the query name.
This special form is useful for query logging in the walled garden’s
authoritative DNS server.
All of the actions specified in all of the individual records in a
policy zone can be overridden with a policy clause in the
response-policy option. An organization using a policy zone provided
by another organization might use this mechanism to redirect domains to
its own walled garden.
GIVEN
The placeholder policy says “do not override but perform the action
specified in the zone.”
DISABLED
The testing override policy causes policy zone records to do nothing
but log what they would have done if the policy zone were not
disabled. The response to the DNS query is written (or not)
according to any triggered policy records that are not disabled.
Disabled policy zones should appear first, because they are often
not logged if a higher-precedence trigger is found first.
PASSTHRU; DROP; TCP-Only; NXDOMAIN; NODATA
These settings each override the corresponding per-record policy.
CNAMEdomain
This causes all RPZ policy records to act as if they were “cname domain”
records.
By default, the actions encoded in a response policy zone are applied
only to queries that ask for recursion (RD=1). That default can be
changed for a single policy zone, or for all response policy zones in a view,
with a recursive-onlyno clause. This feature is useful for serving
the same zone files both inside and outside an RFC 1918 cloud and using
RPZ to delete answers that would otherwise contain RFC 1918 values on
the externally visible name server or view.
Also by default, RPZ actions are applied only to DNS requests that
either do not request DNSSEC metadata (DO=0) or when no DNSSEC records
are available for the requested name in the original zone (not the response
policy zone). This default can be changed for all response policy zones
in a view with a break-dnssecyes clause. In that case, RPZ actions
are applied regardless of DNSSEC. The name of the clause option reflects
the fact that results rewritten by RPZ actions cannot verify.
No DNS records are needed for a QNAME or Client-IP trigger; the name or
IP address itself is sufficient, so in principle the query name need not
be recursively resolved. However, not resolving the requested name can
leak the fact that response policy rewriting is in use, and that the name
is listed in a policy zone, to operators of servers for listed names. To
prevent that information leak, by default any recursion needed for a
request is done before any policy triggers are considered. Because
listed domains often have slow authoritative servers, this behavior can
cost significant time. The qname-wait-recurseno option overrides
the default and enables that behavior when recursion cannot change a
non-error response. The option does not affect QNAME or client-IP
triggers in policy zones listed after other zones containing IP, NSIP,
and NSDNAME triggers, because those may depend on the A, AAAA, and NS
records that would be found during recursive resolution. It also does
not affect DNSSEC requests (DO=1) unless break-dnssecyes is in use,
because the response would depend on whether RRSIG records were
found during resolution. Using this option can cause error responses
such as SERVFAIL to appear to be rewritten, since no recursion is being
done to discover problems at the authoritative server.
The dnsrps-enableyes option turns on the DNS Response Policy Service
(DNSRPS) interface, if it has been compiled in named using
configure--enable-dnsrps.
The dnsrps-options block provides additional RPZ configuration
settings, which are passed through to the DNSRPS provider library.
Multiple DNSRPS settings in an dnsrps-options string should be
separated with semi-colons (;). The DNSRPS provider, librpz, is passed a
configuration string consisting of the dnsrps-options text,
concatenated with settings derived from the response-policy
statement.
Note: the dnsrps-options text should only include configuration
settings that are specific to the DNSRPS provider. For example, the
DNSRPS provider from Farsight Security takes options such as
dnsrpzd-conf, dnsrpzd-sock, and dnzrpzd-args (for details of
these options, see the librpz documentation). Other RPZ
configuration settings could be included in dnsrps-options as well,
but if named were switched back to traditional RPZ by setting
dnsrps-enable to “no”, those options would be ignored.
The TTL of a record modified by RPZ policies is set from the TTL of the
relevant record in the policy zone. It is then limited to a maximum value.
The max-policy-ttl clause changes the maximum number of seconds from its
default of 5. For convenience, TTL-style time-unit suffixes may be used
to specify the value. It also accepts ISO 8601 duration formats.
For example, an administrator might use this option statement:
$TTL 1H
@ SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
NS LOCALHOST.
; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com CNAME . ; NXDOMAIN policy
*.nxdomain.domain.com CNAME . ; NXDOMAIN policy
nodata.domain.com CNAME *. ; NODATA policy
*.nodata.domain.com CNAME *. ; NODATA policy
bad.domain.com A 10.0.0.1 ; redirect to a walled garden
AAAA 2001:2::1
bzone.domain.com CNAME garden.example.com.
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com CNAME rpz-passthru.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com CNAME *.garden.example.com.
; IP policy records that rewrite all responses containing A records in 127/8
; except 127.0.0.1
8.0.0.0.127.rpz-ip CNAME .
32.1.0.0.127.rpz-ip CNAME rpz-passthru.
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname CNAME .
48.zz.2.2001.rpz-nsip CNAME .
; auto-reject and auto-accept some DNS clients
112.zz.2001.rpz-client-ip CNAME rpz-drop.
8.0.0.0.127.rpz-client-ip CNAME rpz-drop.
; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip CNAME rpz-tcp-only.
example.com CNAME rpz-tcp-only.
*.example.com CNAME rpz-tcp-only.
RPZ can affect server performance. Each configured response policy zone
requires the server to perform one to four additional database lookups
before a query can be answered. For example, a DNS server with four
policy zones, each with all four kinds of response triggers (QNAME, IP,
NSIP, and NSDNAME), requires a total of 17 times as many database lookups
as a similar DNS server with no response policy zones. A BIND 9 server
with adequate memory and one response policy zone with QNAME and IP
triggers might achieve a maximum queries-per-second (QPS) rate about 20%
lower. A server with four response policy zones with QNAME and IP
triggers might have a maximum QPS rate about 50% lower.
Responses rewritten by RPZ are counted in the RPZRewrites
statistics.
The log clause can be used to optionally turn off rewrite logging
for a particular response policy zone. By default, all rewrites are
logged.
The add-soa option controls whether the RPZ’s SOA record is added to
the section for traceback of changes from this zone.
This can be set at the individual policy zone level or at the
response-policy level. The default is yes.
Updates to RPZ zones are processed asynchronously; if there is more than
one update pending they are bundled together. If an update to a RPZ zone
(for example, via IXFR) happens less than min-update-interval
seconds after the most recent update, the changes are not
carried out until this interval has elapsed. The default is 60
seconds. For convenience, TTL-style time-unit suffixes may be used to
specify the value. It also accepts ISO 8601 duration formats.
Excessive, almost-identical UDP responses can be controlled by
configuring a rate-limit clause in an options or view
statement. This mechanism keeps authoritative BIND 9 from being used to
amplify reflection denial-of-service (DoS) attacks. Short BADCOOKIE errors or
truncated (TC=1) responses can be sent to provide rate-limited responses to
legitimate clients within a range of forged, attacked IP addresses.
Legitimate clients react to dropped responses by retrying,
to BADCOOKIE errors by including a server cookie when retrying,
and to truncated responses by switching to TCP.
This mechanism is intended for authoritative DNS servers. It can be used
on recursive servers, but can slow applications such as SMTP servers
(mail receivers) and HTTP clients (web browsers) that repeatedly request
the same domains. When possible, closing “open” recursive servers is
better.
Response rate limiting uses a “credit” or “token bucket” scheme. Each
combination of identical response and client has a conceptual “account”
that earns a specified number of credits every second. A prospective
response debits its account by one. Responses are dropped or truncated
while the account is negative. Responses are tracked within a rolling
window of time which defaults to 15 seconds, but which can be configured with
the window option to any value from 1 to 3600 seconds (1 hour). The
account cannot become more positive than the per-second limit or more
negative than window times the per-second limit. When the specified
number of credits for a class of responses is set to 0, those responses
are not rate-limited.
The notions of “identical response” and “DNS client” for rate limiting
are not simplistic. All responses to an address block are counted as if
to a single client. The prefix lengths of address blocks are specified
with ipv4-prefix-length (default 24) and ipv6-prefix-length
(default 56).
All non-empty responses for a valid domain name (qname) and record type
(qtype) are identical and have a limit specified with
responses-per-second (default 0 or no limit). All valid wildcard
domain names are interpreted as the zone’s origin name concatenated to
the “*” name. All empty (NODATA) responses for a valid domain,
regardless of query type, are identical. Responses in the NODATA class
are limited by nodata-per-second (default responses-per-second).
Requests for any and all undefined subdomains of a given valid domain
result in NXDOMAIN errors, and are identical regardless of query type.
They are limited by nxdomains-per-second (default
responses-per-second). This controls some attacks using random
names, but can be relaxed or turned off (set to 0) on servers that
expect many legitimate NXDOMAIN responses, such as from anti-spam
rejection lists. Referrals or delegations to the server of a given
domain are identical and are limited by referrals-per-second
(default responses-per-second).
Responses generated from local wildcards are counted and limited as if
they were for the parent domain name. This controls flooding using
random.wild.example.com.
All requests that result in DNS errors other than NXDOMAIN, such as
SERVFAIL and FORMERR, are identical regardless of requested name (qname)
or record type (qtype). This controls attacks using invalid requests or
distant, broken authoritative servers. By default the limit on errors is
the same as the responses-per-second value, but it can be set
separately with errors-per-second.
Many attacks using DNS involve UDP requests with forged source
addresses. Rate limiting prevents the use of BIND 9 to flood a network
with responses to requests with forged source addresses, but could let a
third party block responses to legitimate requests. There is a mechanism
that can answer some legitimate requests from a client whose address is
being forged in a flood. Setting slip to 2 (its default) causes
every other UDP request without a valid server cookie to be answered with
a small response. The small size and reduced frequency, and resulting lack of
amplification, of “slipped” responses make them unattractive for
reflection DoS attacks. slip must be between 0 and 10. A value of 0
does not “slip”; no small responses are sent due to rate limiting. Rather,
all responses are dropped. A value of 1 causes every response to slip;
values between 2 and 10 cause every nth response to slip.
If the request included a client cookie, then a “slipped” response is
a BADCOOKIE error with a server cookie, which allows a legitimate client
to include the server cookie to be exempted from the rate limiting
when it retries the request.
If the request did not include a cookie, then a “slipped” response is
a truncated (TC=1) response, which prompts a legitimate client to
switch to TCP and thus be exempted from the rate limiting. Some error
responses, including REFUSED and SERVFAIL, cannot be replaced with
truncated responses and are instead leaked at the slip rate.
(Note: dropped responses from an authoritative server may reduce the
difficulty of a third party successfully forging a response to a
recursive resolver. The best security against forged responses is for
authoritative operators to sign their zones using DNSSEC and for
resolver operators to validate the responses. When this is not an
option, operators who are more concerned with response integrity than
with flood mitigation may consider setting slip to 1, causing all
rate-limited responses to be truncated rather than dropped. This reduces
the effectiveness of rate-limiting against reflection attacks.)
When the approximate query-per-second rate exceeds the qps-scale
value, the responses-per-second, errors-per-second,
nxdomains-per-second, and all-per-second values are reduced by
the ratio of the current rate to the qps-scale value. This feature
can tighten defenses during attacks. For example, with
qps-scale250;responses-per-second20; and a total query rate of
1000 queries/second for all queries from all DNS clients including via
TCP, then the effective responses/second limit changes to (250/1000)*20,
or 5. Responses to requests that included a valid server cookie,
and responses sent via TCP, are not limited but are counted to compute
the query-per-second rate.
Communities of DNS clients can be given their own parameters or no
rate limiting by putting rate-limit statements in view statements
instead of in the global option statement. A rate-limit statement
in a view replaces, rather than supplements, a rate-limit
statement among the main options. DNS clients within a view can be
exempted from rate limits with the exempt-clients clause.
UDP responses of all kinds can be limited with the all-per-second
phrase. This rate limiting is unlike the rate limiting provided by
responses-per-second, errors-per-second, and
nxdomains-per-second on a DNS server, which are often invisible to
the victim of a DNS reflection attack. Unless the forged requests of the
attack are the same as the legitimate requests of the victim, the
victim’s requests are not affected. Responses affected by an
all-per-second limit are always dropped; the slip value has no
effect. An all-per-second limit should be at least 4 times as large
as the other limits, because single DNS clients often send bursts of
legitimate requests. For example, the receipt of a single mail message
can prompt requests from an SMTP server for NS, PTR, A, and AAAA records
as the incoming SMTP/TCP/IP connection is considered. The SMTP server
can need additional NS, A, AAAA, MX, TXT, and SPF records as it
considers the SMTP MailFrom command. Web browsers often repeatedly
resolve the same names that are duplicated in HTML <IMG> tags in a page.
all-per-second is similar to the rate limiting offered by firewalls
but is often inferior. Attacks that justify ignoring the contents of DNS
responses are likely to be attacks on the DNS server itself. They
usually should be discarded before the DNS server spends resources making
TCP connections or parsing DNS requests, but that rate limiting must be
done before the DNS server sees the requests.
The maximum size of the table used to track requests and rate-limit
responses is set with max-table-size. Each entry in the table is
between 40 and 80 bytes. The table needs approximately as many entries
as the number of requests received per second. The default is 20,000. To
reduce the cold start of growing the table, min-table-size (default 500)
can set the minimum table size. Enable rate-limit category
logging to monitor expansions of the table and inform choices for the
initial and maximum table size.
Use log-onlyyes to test rate-limiting parameters without actually
dropping any requests.
Responses dropped by rate limits are included in the RateDropped and
QryDropped statistics. Responses that are truncated by rate limits are
included in RateSlipped and RespTruncated.
With either method, when named gets an NXDOMAIN response it examines a
separate namespace to see if the NXDOMAIN response should be replaced
with an alternative response.
With a redirect zone (zone"."{typeredirect;};), the data used
to replace the NXDOMAIN is held in a single zone which is not part of
the normal namespace. All the redirect information is contained in the
zone; there are no delegations.
With a redirect namespace (option{nxdomain-redirect<suffix>};),
the data used to replace the NXDOMAIN is part of the normal namespace
and is looked up by appending the specified suffix to the original
query name. This roughly doubles the cache required to process
NXDOMAIN responses, as both the original NXDOMAIN response and the
replacement data (or an NXDOMAIN indicating that there is no
replacement) must be stored.
If both a redirect zone and a redirect namespace are configured, the
redirect zone is tried first.
The server statement defines characteristics to be associated with a
remote name server. If a prefix length is specified, then a range of
servers is covered. Only the most specific server clause applies,
regardless of the order in named.conf.
The server statement can occur at the top level of the configuration
file or inside a view statement. If a view statement contains
one or more server statements, only those apply to the view and any
top-level ones are ignored. If a view contains no server statements,
any top-level server statements are used as defaults.
If a remote server is giving out bad data, marking it
as bogus prevents further queries to it. The default value of
bogus is no.
The provide-ixfr clause determines whether the local server, acting
as primary, responds with an incremental zone transfer when the given
remote server, a secondary, requests it. If set to yes, incremental
transfer is provided whenever possible. If set to no, all
transfers to the remote server are non-incremental. If not set, the
value of the provide-ixfr option in the view or global options block
is used as a default.
The request-ixfr clause determines whether the local server, acting
as a secondary, requests incremental zone transfers from the given
remote server, a primary. If not set, the value of the request-ixfr
option in the view or global options block is used as a default. It may
also be set in the zone block; if set there, it overrides the
global or view setting for that zone.
IXFR requests to servers that do not support IXFR automatically
fall back to AXFR. Therefore, there is no need to manually list which
servers support IXFR and which ones do not; the global default of
yes should always work. The purpose of the provide-ixfr and
request-ixfr clauses is to make it possible to disable the use of
IXFR even when both primary and secondary claim to support it: for example, if
one of the servers is buggy and crashes or corrupts data when IXFR is
used.
The request-expire clause determines whether the local server, when
acting as a secondary, requests the EDNS EXPIRE value. The EDNS EXPIRE
value indicates the remaining time before the zone data expires and
needs to be refreshed. This is used when a secondary server transfers
a zone from another secondary server; when transferring from the
primary, the expiration timer is set from the EXPIRE field of the SOA
record instead. The default is yes.
The edns clause determines whether the local server attempts to
use EDNS when communicating with the remote server. The default is
yes.
The edns-udp-size option sets the EDNS UDP size that is advertised
by named when querying the remote server. Valid values are 512 to
4096 bytes; values outside this range are silently adjusted to the
nearest value within it. This option is useful when
advertising a different value to this server than the value advertised
globally: for example, when there is a firewall at the remote site that
is blocking large replies. Note: currently, this sets a single UDP size
for all packets sent to the server; named does not deviate from this
value. This differs from the behavior of edns-udp-size in
options or view statements, where it specifies a maximum value.
The server statement behavior may be brought into conformance with
the options/view behavior in future releases.
The edns-version option sets the maximum EDNS VERSION that is
sent to the server(s) by the resolver. The actual EDNS version sent is
still subject to normal EDNS version-negotiation rules (see RFC 6891),
the maximum EDNS version supported by the server, and any other
heuristics that indicate that a lower version should be sent. This
option is intended to be used when a remote server reacts badly to a
given EDNS version or higher; it should be set to the highest version
the remote server is known to support. Valid values are 0 to 255; higher
values are silently adjusted. This option is not needed until
higher EDNS versions than 0 are in use.
The max-udp-size option sets the maximum EDNS UDP message size
named sends. Valid values are 512 to 4096 bytes; values outside
this range are silently adjusted. This option is useful when
there is a firewall that is blocking large replies from
named.
The padding option adds EDNS Padding options to outgoing messages,
increasing the packet size to a multiple of the specified block size.
Valid block sizes range from 0 (the default, which disables the use of
EDNS Padding) to 512 bytes. Larger values are reduced to 512, with a
logged warning. Note: this option is not currently compatible with no
TSIG or SIG(0), as the EDNS OPT record containing the padding would have
to be added to the packet after it had already been signed.
The tcp-only option sets the transport protocol to TCP. The default
is to use the UDP transport and to fallback on TCP only when a truncated
response is received.
The tcp-keepalive option adds EDNS TCP keepalive to messages sent
over TCP. Note that currently idle timeouts in responses are ignored.
The server supports two zone transfer methods. The first,
one-answer, uses one DNS message per resource record transferred.
many-answers packs as many resource records as possible into a single
message, which is more efficient.
It is possible to specify which method to use for a server via the
transfer-format option; if not set there, the
transfer-format specified by the options statement is used.
transfers is used to limit the number of concurrent inbound zone
transfers from the specified server. If no transfers clause is
specified, the limit is set according to the transfers-per-ns
option.
The keys clause identifies a key_id defined by the key
statement, to be used for transaction security (see TSIG)
when talking to the remote server. When a request is sent to the remote
server, a request signature is generated using the key specified
here and appended to the message. A request originating from the remote
server is not required to be signed by this key.
Only a single key per server is currently supported.
The transfer-source and transfer-source-v6 clauses specify the
IPv4 and IPv6 source address, respectively, to be used for zone transfer with the
remote server. For an IPv4 remote server, only
transfer-source can be specified. Similarly, for an IPv6 remote
server, only transfer-source-v6 can be specified. For more details,
see the description of transfer-source and transfer-source-v6 in
Zone Transfers.
The notify-source and notify-source-v6 clauses specify the IPv4
and IPv6 source address, respectively, to be used for notify messages sent to remote
servers. For an IPv4 remote server, only notify-source
can be specified. Similarly, for an IPv6 remote server, only
notify-source-v6 can be specified.
The query-source and query-source-v6 clauses specify the IPv4
and IPv6 source address, respectively, to be used for queries sent to remote servers.
For an IPv4 remote server, only query-source can be
specified. Similarly, for an IPv6 remote server, only
query-source-v6 can be specified.
The request-nsid clause determines whether the local server adds
an NSID EDNS option to requests sent to the server. This overrides
request-nsid set at the view or option level.
The send-cookie clause determines whether the local server adds
a COOKIE EDNS option to requests sent to the server. This overrides
send-cookie set at the view or option level. The named server
may determine that COOKIE is not supported by the remote server and not
add a COOKIE EDNS option to requests.
statistics-channels Statement Definition and Usage
The statistics-channels statement declares communication channels to
be used by system administrators to get access to statistics information
on the name server.
This statement is intended to be flexible to support multiple communication
protocols in the future, but currently only HTTP access is supported. It
requires that BIND 9 be compiled with libxml2 and/or json-c (also known
as libjson0); the statistics-channels statement is still accepted
even if it is built without the library, but any HTTP access fails
with an error.
An inet control channel is a TCP socket listening at the specified
ip_port on the specified ip_addr, which can be an IPv4 or IPv6
address. An ip_addr of * (asterisk) is interpreted as the IPv4
wildcard address; connections are accepted on any of the system’s
IPv4 addresses. To listen on the IPv6 wildcard address, use an
ip_addr of ::.
If no port is specified, port 80 is used for HTTP channels. The asterisk
(*) cannot be used for ip_port.
Attempts to open a statistics channel are restricted by the
optional allow clause. Connections to the statistics channel are
permitted based on the address_match_list. If no allow clause is
present, named accepts connection attempts from any address. Since
the statistics may contain sensitive internal information, the source of
connection requests must be restricted appropriately so that only
trusted parties can access the statistics channel.
Gathering data exposed by the statistics channel locks various subsystems in
named, which could slow down query processing if statistics data is
requested too often.
An issue in the statistics channel would be considered a security issue
only if it could be exploited by unprivileged users circumventing the access
control list. In other words, any issue in the statistics channel that could be
used to access information unavailable otherwise, or to crash named, is
not considered a security issue if it can be avoided through the
use of a secure configuration.
If no statistics-channels statement is present, named does not
open any communication channels.
The statistics are available in various formats and views, depending on
the URI used to access them. For example, if the statistics channel is
configured to listen on 127.0.0.1 port 8888, then the statistics are
accessible in XML format at http://127.0.0.1:8888/ or
http://127.0.0.1:8888/xml. A CSS file is included, which can format the
XML statistics into tables when viewed with a stylesheet-capable
browser, and into charts and graphs using the Google Charts API when
using a JavaScript-capable browser.
The trust-anchors statement defines DNSSEC trust anchors. DNSSEC is
described in DNSSEC.
A trust anchor is defined when the public key or public key digest for a non-authoritative
zone is known but cannot be securely obtained through DNS, either
because it is the DNS root zone or because its parent zone is unsigned.
Once a key or digest has been configured as a trust anchor, it is treated as if it
has been validated and proven secure.
The resolver attempts DNSSEC validation on all DNS data in subdomains of
configured trust anchors. Validation below specified names can be
temporarily disabled by using rndcnta, or permanently disabled with
the validate-except option.
All keys listed in trust-anchors, and their corresponding zones, are
deemed to exist regardless of what parent zones say. Only keys
configured as trust anchors are used to validate the DNSKEY RRset for
the corresponding name. The parent’s DS RRset is not used.
trust-anchors may be set at the top level of named.conf or within
a view. If it is set in both places, the configurations are additive;
keys defined at the top level are inherited by all views, but keys
defined in a view are only used within that view.
The trust-anchors statement can contain
multiple trust-anchor entries, each consisting of a
domain name, followed by an “anchor type” keyword indicating
the trust anchor’s format, followed by the key or digest data.
If the anchor type is static-key or
initial-key, then it is followed with the
key’s flags, protocol, and algorithm, plus the Base64 representation
of the public key data. This is identical to the text
representation of a DNSKEY record. Spaces, tabs, newlines, and
carriage returns are ignored in the key data, so the
configuration may be split into multiple lines.
If the anchor type is static-ds or
initial-ds, it is followed with the
key tag, algorithm, digest type, and the hexadecimal
representation of the key digest. This is identical to the
text representation of a DS record. Spaces, tabs, newlines,
and carriage returns are ignored.
Trust anchors configured with the
static-key or static-ds
anchor types are immutable, while keys configured with
initial-key or initial-ds
can be kept up-to-date automatically, without intervention from the resolver operator.
(static-key keys are identical to keys configured using the
deprecated trusted-keys statement.)
Suppose, for example, that a zone’s key-signing key was compromised, and
the zone owner had to revoke and replace the key. A resolver which had
the original key
configured using static-key or
static-ds would be unable to validate
this zone any longer; it would reply with a SERVFAIL response
code. This would continue until the resolver operator had
updated the trust-anchors statement with
the new key.
If, however, the trust anchor had been configured using
initial-key or initial-ds
instead, the zone owner could add a “stand-by” key to
the zone in advance. named would store
the stand-by key, and when the original key was revoked,
named would be able to transition smoothly
to the new key. It would also recognize that the old key had
been revoked and cease using that key to validate answers,
minimizing the damage that the compromised key could do.
This is the process used to keep the ICANN root DNSSEC key
up-to-date.
Whereas static-key and
static-ds trust anchors continue
to be trusted until they are removed from
named.conf, an
initial-key or initial-ds
is only trusted once: for as long as it
takes to load the managed key database and start the
RFC 5011 key maintenance process.
It is not possible to mix static with initial trust anchors
for the same domain name.
The first time named runs with an
initial-key or initial-ds
configured in named.conf, it fetches the
DNSKEY RRset directly from the zone apex,
and validates it
using the trust anchor specified in trust-anchors.
If the DNSKEY RRset is validly signed by a key matching
the trust anchor, then it is used as the basis for a new
managed-keys database.
From that point on, whenever named runs, it sees the initial-key or initial-ds
listed in trust-anchors, checks to make sure RFC 5011 key maintenance
has already been initialized for the specified domain, and if so,
simply moves on. The key specified in the trust-anchors statement is
not used to validate answers; it is superseded by the key or keys stored
in the managed-keys database.
The next time named runs after an initial-key or initial-ds has been removed
from the trust-anchors statement (or changed to a static-key or static-ds), the
corresponding zone is removed from the managed-keys database, and
RFC 5011 key maintenance is no longer used for that domain.
In the current implementation, the managed-keys database is stored as a
master-format zone file.
On servers which do not use views, this file is named
managed-keys.bind. When views are in use, there is a separate
managed-keys database for each view; the filename is the view name
(or, if a view name contains characters which would make it illegal as a
filename, a hash of the view name), followed by the suffix .mkeys.
When the key database is changed, the zone is updated. As with any other
dynamic zone, changes are written into a journal file, e.g.,
managed-keys.bind.jnl or internal.mkeys.jnl. Changes are
committed to the primary file as soon as possible afterward,
usually within 30 seconds. Whenever named is using
automatic key maintenance, the zone file and journal file can be
expected to exist in the working directory. (For this reason, among
others, the working directory should be always be writable by
named.)
If the dnssec-validation option is set to auto, named
automatically initializes an initial-key for the root zone. The key
that is used to initialize the key-maintenance process is stored in
bind.keys; the location of this file can be overridden with the
bindkeys-file option. As a fallback in the event no bind.keys
can be found, the initializing key is also compiled directly into
named.
The dnssec-policy statement defines a key and signing policy (KASP)
for zones.
A KASP determines how one or more zones are signed with DNSSEC. For
example, it specifies how often keys should roll, which cryptographic
algorithms to use, and how often RRSIG records need to be refreshed.
Keys are not shared among zones, which means that one set of keys per
zone is generated even if they have the same policy. If multiple views
are configured with different versions of the same zone, each separate
version uses the same set of signing keys.
Multiple key and signing policies can be configured. To attach a policy
to a zone, add a dnssec-policy option to the zone statement,
specifying the name of the policy that should be used.
The dnssec-policy statement requires dynamic DNS to be set up, or
inline-signing to be enabled.
If inline-signing is enabled, this means that a signed version of the
zone is maintained separately and is written out to a different file on disk
(the zone’s filename plus a .signed extension).
If the zone is dynamic because it is configured with an update-policy or
allow-update, the DNSSEC records are written to the filename set in the
original zone’s file, unless inline-signing is explicitly set.
Key rollover timing is computed for each key according to the key
lifetime defined in the KASP. The lifetime may be modified by zone TTLs
and propagation delays, to prevent validation failures. When a key
reaches the end of its lifetime, named generates and publishes a new
key automatically, then deactivates the old key and activates the new
one; finally, the old key is retired according to a computed schedule.
Zone-signing key (ZSK) rollovers require no operator input. Key-signing
key (KSK) and combined-signing key (CSK) rollovers require action to be
taken to submit a DS record to the parent. Rollover timing for KSKs and
CSKs is adjusted to take into account delays in processing and
propagating DS updates.
There are two predefined dnssec-policy names: none and
default. Setting a zone’s policy to none is the same as not
setting dnssec-policy at all; the zone is not signed. Policy
default causes the zone to be signed with a single combined-signing
key (CSK) using algorithm ECDSAP256SHA256; this key has an unlimited
lifetime. (A verbose copy of this policy may be found in the source
tree, in the file doc/misc/dnssec-policy.default.conf.)
Note
The default signing policy may change in future releases.
This could require changes to a signing policy when upgrading to a
new version of BIND. Check the release notes carefully when
upgrading to be informed of such changes. To prevent policy changes
on upgrade, use an explicitly defined dnssec-policy, rather than
default.
If a dnssec-policy statement is modified and the server restarted or
reconfigured, named attempts to change the policy smoothly from the
old one to the new. For example, if the key algorithm is changed, then
a new key is generated with the new algorithm, and the old algorithm is
retired when the existing key’s lifetime ends.
Note
Rolling to a new policy while another key rollover is already
in progress is not yet supported, and may result in unexpected
behavior.
The following options can be specified in a dnssec-policy statement:
dnskey-ttl
This indicates the TTL to use when generating DNSKEY resource
records. The default is 1 hour (3600 seconds).
keys
This is a list specifying the algorithms and roles to use when
generating keys and signing the zone. Entries in this list do not
represent specific DNSSEC keys, which may be changed on a regular
basis, but the roles that keys play in the signing policy. For
example, configuring a KSK of algorithm RSASHA256 ensures that the
DNSKEY RRset always includes a key-signing key for that algorithm.
Here is an example (for illustration purposes only) of some possible
entries in a keys list:
This example specifies that three keys should be used in the zone.
The first token determines which role the key plays in signing
RRsets. If set to ksk, then this is a key-signing key; it has
the KSK flag set and is only used to sign DNSKEY, CDS, and CDNSKEY
RRsets. If set to zsk, this is a zone-signing key; the KSK flag
is unset, and the key signs all RRsets except DNSKEY, CDS, and
CDNSKEY. If set to csk, the key has the KSK flag set and is
used to sign all RRsets.
An optional second token determines where the key is stored.
Currently, keys can only be stored in the configured
key-directory. This token may be used in the future to store
keys in hardware security modules or separate directories.
The lifetime parameter specifies how long a key may be used
before rolling over. In the example above, the first key has an
unlimited lifetime, the second key may be used for 30 days, and the
third key has a rather peculiar lifetime of 6 months, 12 hours, 3
minutes, and 15 seconds. A lifetime of 0 seconds is the same as
unlimited.
Note that the lifetime of a key may be extended if retiring it too
soon would cause validation failures. For example, if the key were
configured to roll more frequently than its own TTL, its lifetime
would automatically be extended to account for this.
The algorithm parameter specifies the key’s algorithm, expressed
either as a string (“rsasha256”, “ecdsa384”, etc.) or as a decimal
number. An optional second parameter specifies the key’s size in
bits. If it is omitted, as shown in the example for the second and
third keys, an appropriate default size for the algorithm is used.
Each KSK/ZSK pair must have the same algorithm. A CSK combines the
functionality of a ZSK and a KSK.
purge-keys
This is the time after when DNSSEC keys that have been deleted from
the zone can be removed from disk. If a key still determined to have
presence (for example in some resolver cache), named will not
remove the key files.
The default is P90D (90 days). Set this option to 0 to never
purge deleted keys.
publish-safety
This is a margin that is added to the pre-publication interval in
rollover timing calculations, to give some extra time to cover
unforeseen events. This increases the time between when keys are
published and when they become active. The default is PT1H (1
hour).
retire-safety
This is a margin that is added to the post-publication interval in
rollover timing calculations, to give some extra time to cover
unforeseen events. This increases the time a key remains published
after it is no longer active. The default is PT1H (1 hour).
signatures-refresh
This determines how frequently an RRSIG record needs to be
refreshed. The signature is renewed when the time until the
expiration time is less than the specified interval. The default is
P5D (5 days), meaning signatures that expire in 5 days or sooner
are refreshed.
signatures-validity
This indicates the validity period of an RRSIG record (subject to
inception offset and jitter). The default is P2W (2 weeks).
signatures-validity-dnskey
This is similar to signatures-validity, but for DNSKEY records.
The default is P2W (2 weeks).
max-zone-ttl
This specifies the maximum permissible TTL value for the zone. When
a zone file is loaded, any record encountered with a TTL higher than
max-zone-ttl causes the zone to be rejected.
This ensures that when rolling to a new DNSKEY, the old key will remain
available until RRSIG records have expired from caches. The
max-zone-ttl option guarantees that the largest TTL in the
zone is no higher than a known and predictable value.
Note
Because map-format files load directly into memory,
this option cannot be used with them.
The default value PT24H (24 hours). A value of zero is treated
as if the default value were in use.
nsec3param
Use NSEC3 instead of NSEC, and optionally set the NSEC3 parameters.
Here is an example of an nsec3 configuration:
nsec3paramiterations5optoutnosalt-length8;
The default is to use NSEC. The iterations, optout, and
salt-length parts are optional, but if not set, the values in
the example above are the default NSEC3 parameters. Note that the
specific salt string is not specified by the user; named creates a salt
of the indicated length.
Warning
Do not use extra iterations, salt, and
opt-out unless their implications are fully understood.
A higher number of iterations causes interoperability problems and opens
servers to CPU-exhausting DoS attacks.
zone-propagation-delay
This is the expected propagation delay from the time when a zone is
first updated to the time when the new version of the zone is served
by all secondary servers. The default is PT5M (5 minutes).
parent-ds-ttl
This is the TTL of the DS RRset that the parent zone uses. The
default is P1D (1 day).
parent-propagation-delay
This is the expected propagation delay from the time when the parent
zone is updated to the time when the new version is served by all of
the parent zone’s name servers. The default is PT1H (1 hour).
BIND has mechanisms in place to facilitate automated KSK rollovers. It
publishes CDS and CDNSKEY records that can be used by the parent zone to
publish or withdraw the zone’s DS records. BIND will query the parental
agents to see if the new DS is actually published before withdrawing the
old DNSSEC key.
Note
The DS response is not validated so it is recommended to set up a
trust relationship with the parental agent. For example, use TSIG to
authenticate the parental agent, or point to a validating resolver.
The following options apply to DS queries sent to parental-agents:
parental-source
parental-source determines which local source address, and optionally
UDP port, is used to send parental DS queries. This statement sets the
parental-source for all zones, but can be overridden on a per-zone or
per-view basis by including a parental-source statement within the
zone or view block in the configuration file.
Warning
Specifying a single port is discouraged, as it removes a layer of
protection against spoofing errors.
Warning
The configured port must not be same as the listening port.
parental-source-v6
This option acts like parental-source, but applies to parental DS
queries sent to IPv6 addresses.
The view statement is a powerful feature of BIND 9 that lets a name
server answer a DNS query differently depending on who is asking. It is
particularly useful for implementing split DNS setups without having to
run multiple servers.
Each view statement defines a view of the DNS namespace that is
seen by a subset of clients. A client matches a view if its source IP
address matches the address_match_list of the view’s
match-clients clause, and its destination IP address matches the
address_match_list of the view’s match-destinations clause. If
not specified, both match-clients and match-destinations default
to matching all addresses. In addition to checking IP addresses,
match-clients and match-destinations can also take keys
which provide an mechanism for the client to select the view. A view can
also be specified as match-recursive-only, which means that only
recursive requests from matching clients match that view. The order
of the view statements is significant; a client request is
resolved in the context of the first view that it matches.
Zones defined within a view statement are only accessible to
clients that match the view. By defining a zone of the same name in
multiple views, different zone data can be given to different clients:
for example, “internal” and “external” clients in a split DNS setup.
Many of the options given in the options statement can also be used
within a view statement, and then apply only when resolving queries
with that view. When no view-specific value is given, the value in the
options statement is used as a default. Also, zone options can have
default values specified in the view statement; these view-specific
defaults take precedence over those in the options statement.
Views are class-specific. If no class is given, class IN is assumed.
Note that all non-IN views must contain a hint zone, since only the IN
class has compiled-in default hints.
If there are no view statements in the config file, a default view
that matches any client is automatically created in class IN. Any
zone statements specified on the top level of the configuration file
are considered to be part of this default view, and the options
statement applies to the default view. If any explicit view
statements are present, all zone statements must occur inside
view statements.
Here is an example of a typical split DNS setup implemented using
view statements:
The type keyword is required for the zone configuration unless
it is an in-view configuration. Its acceptable values are:
primary (or master), secondary (or slave), mirror,
hint, stub, static-stub, forward, redirect,
or delegation-only.
primary
A primary zone has a master copy of the data for the zone and is able
to provide authoritative answers for it. Type master is a synonym
for primary.
secondary
A secondary zone is a replica of a primary zone. Type slave is a
synonym for secondary. The primaries list specifies one or more IP
addresses of primary servers that the secondary contacts to update
its copy of the zone. Primaries list elements can
also be names of other primaries lists. By default,
transfers are made from port 53 on the servers;
this can be changed for all servers by specifying
a port number before the list of IP addresses,
or on a per-server basis after the IP address.
Authentication to the primary can also be done with
per-server TSIG keys. If a file is specified, then the
replica is written to this file
whenever the zone
is changed, and reloaded from this file on a server
restart. Use of a file is recommended, since it
often speeds server startup and eliminates a
needless waste of bandwidth. Note that for large
numbers (in the tens or hundreds of thousands) of
zones per server, it is best to use a two-level
naming scheme for zone filenames. For example,
a secondary server for the zone
example.com might place
the zone contents into a file called
ex/example.com, where
ex/ is just the first two
letters of the zone name. (Most operating systems
behave very slowly if there are 100000 files in a single directory.)
mirror
A mirror zone is similar to a zone of type secondary, except its
data is subject to DNSSEC validation before being used in answers.
Validation is applied to the entire zone during the zone transfer
process, and again when the zone file is loaded from disk upon
restarting named. If validation of a new version of a mirror zone
fails, a retransfer is scheduled; in the meantime, the most recent
correctly validated version of that zone is used until it either
expires or a newer version validates correctly. If no usable zone
data is available for a mirror zone, due to either transfer failure
or expiration, traditional DNS recursion is used to look up the
answers instead. Mirror zones cannot be used in a view that does not
have recursion enabled.
Answers coming from a mirror zone look almost exactly like answers
from a zone of type secondary, with the notable exceptions that
the AA bit (“authoritative answer”) is not set, and the AD bit
(“authenticated data”) is.
Mirror zones are intended to be used to set up a fast local copy of
the root zone (see RFC 8806). A default list of primary servers
for the IANA root zone is built into named, so its mirroring can
be enabled using the following configuration:
zone"."{typemirror;};
Mirror zone validation always happens for the entire zone contents.
This ensures that each version of the zone used by the resolver is
fully self-consistent with respect to DNSSEC. For incoming mirror
zone IXFRs, every revision of the zone contained in the IXFR sequence
is validated independently, in the order in which the zone revisions
appear on the wire. For this reason, it might be useful to force use
of AXFR for mirror zones by setting request-ixfrno; for the
relevant zone (or view). Other, more efficient zone verification
methods may be added in the future.
To make mirror zone contents persist between named restarts, use
the file option.
Mirroring a zone other than root requires an explicit list of primary
servers to be provided using the primaries option (see
primaries Statement Grammar for details), and a key-signing key (KSK)
for the specified zone to be explicitly configured as a trust anchor
(see trust-anchors Statement Definition and Usage).
When configuring NOTIFY for a mirror zone, only notifyno; and
notifyexplicit; can be used at the zone level; any other
notify setting at the zone level is a configuration error. Using
any other notify setting at the options or view level
causes that setting to be overridden with notifyexplicit; for
the mirror zone. The global default for the notify option is
yes, so mirror zones are by default configured with notifyexplicit;.
Outgoing transfers of mirror zones are disabled by default but may be
enabled using allow-transfer.
Note
Use of this zone type with any zone other than the root should be
considered experimental and may cause performance issues,
especially for zones that are large and/or frequently updated.
hint
The initial set of root name servers is specified using a hint zone.
When the server starts, it uses the root hints to find a root name
server and get the most recent list of root name servers. If no hint zone
is specified for class IN, the server uses a compiled-in default set of
root servers hints. Classes other than IN have no built-in default hints.
stub
A stub zone is similar to a secondary zone, except that it replicates only
the NS records of a primary zone instead of the entire zone. Stub zones
are not a standard part of the DNS; they are a feature specific to the
BIND implementation.
Stub zones can be used to eliminate the need for a glue NS record in a parent
zone, at the expense of maintaining a stub zone entry and a set of name
server addresses in named.conf. This usage is not recommended for
new configurations, and BIND 9 supports it only in a limited way. If a BIND 9
primary, serving a parent zone, has child stub
zones configured, all the secondary servers for the parent zone also need to
have the same child stub zones configured.
Stub zones can also be used as a way to force the resolution of a given
domain to use a particular set of authoritative servers. For example, the
caching name servers on a private network using RFC 1918 addressing may be
configured with stub zones for 10.in-addr.arpa to use a set of
internal name servers as the authoritative servers for that domain.
static-stub
A static-stub zone is similar to a stub zone, with the following
exceptions: the zone data is statically configured, rather than
transferred from a primary server; and when recursion is necessary for a query
that matches a static-stub zone, the locally configured data (name server
names and glue addresses) is always used, even if different authoritative
information is cached.
Zone data is configured via the server-addresses and server-names
zone options.
The zone data is maintained in the form of NS and (if necessary) glue A or
AAAA RRs internally, which can be seen by dumping zone databases with
rndcdumpdb-all. The configured RRs are considered local configuration
parameters rather than public data. Non-recursive queries (i.e., those
with the RD bit off) to a static-stub zone are therefore prohibited and
are responded to with REFUSED.
Since the data is statically configured, no zone maintenance action takes
place for a static-stub zone. For example, there is no periodic refresh
attempt, and an incoming notify message is rejected with an rcode
of NOTAUTH.
Each static-stub zone is configured with internally generated NS and (if
necessary) glue A or AAAA RRs.
forward
A forward zone is a way to configure forwarding on a per-domain basis.
A zone statement of type forward can contain a forward and/or
forwarders statement, which applies to queries within the domain
given by the zone name. If no forwarders statement is present, or an
empty list for forwarders is given, then no forwarding is done
for the domain, canceling the effects of any forwarders in the options
statement. Thus, to use this type of zone to change the
behavior of the global forward option (that is, “forward first” to,
then “forward only”, or vice versa), but use the same servers as set
globally, re-specify the global forwarders.
redirect
Redirect zones are used to provide answers to queries when normal
resolution would result in NXDOMAIN being returned. Only one redirect zone
is supported per view. allow-query can be used to restrict which
clients see these answers.
If the client has requested DNSSEC records (DO=1) and the NXDOMAIN response
is signed, no substitution occurs.
To redirect all NXDOMAIN responses to 100.100.100.2 and
2001:ffff:ffff::100.100.100.2, configure a type redirect zone
named “.”, with the zone file containing wildcard records that point to
the desired addresses: *.INA100.100.100.2 and
*.INAAAA2001:ffff:ffff::100.100.100.2.
As another example, to redirect all Spanish names (under .ES), use similar entries
but with the names *.ES. instead of *.. To redirect all commercial
Spanish names (under COM.ES), use wildcard entries
called *.COM.ES..
Note that the redirect zone supports all possible types; it is not
limited to A and AAAA records.
If a redirect zone is configured with a primaries option, then it is
transferred in as if it were a secondary zone. Otherwise, it is loaded from a
file as if it were a primary zone.
Because redirect zones are not referenced directly by name, they are not
kept in the zone lookup table with normal primary and secondary zones. To reload
a redirect zone, use rndcreload-redirect; to retransfer a
redirect zone configured as a secondary, use rndcretransfer-redirect.
When using rndcreload without specifying a zone name, redirect
zones are reloaded along with other zones.
delegation-only
This zone type is used to enforce the delegation-only status of infrastructure
zones (e.g., COM, NET, ORG). Any answer that is received without an
explicit or implicit delegation in the authority section is treated
as NXDOMAIN. This does not apply to the zone apex, and should not be
applied to leaf zones.
delegation-only has no effect on answers received from forwarders.
When using multiple views, a primary or secondary zone configured
in one view can be referenced in a subsequent view. This allows both views
to use the same zone without the overhead of loading it more than once. This
is configured using a zone statement, with an in-view option
specifying the view in which the zone is defined. A zone statement
containing in-view does not need to specify a type, since that is part
of the zone definition in the other view.
The zone’s name may optionally be followed by a class. If a class is not
specified, class IN (for Internet) is assumed. This is correct
for the vast majority of cases.
The hesiod class is named for an information service from MIT’s
Project Athena. It was used to share information about various systems
databases, such as users, groups, printers, and so on. The keyword HS
is a synonym for hesiod.
Another MIT development is Chaosnet, a LAN protocol created in the
mid-1970s. Zone data for it can be specified with the CHAOS class.
See the description of allow-update-forwarding in Access Control.
also-notify
This option is only meaningful if notify is active for this zone. The set of
machines that receive a DNSNOTIFY message for this zone is
made up of all the listed name servers (other than the primary)
for the zone, plus any IP addresses specified with
also-notify. A port may be specified with each also-notify
address to send the notify messages to a port other than the default
of 53. A TSIG key may also be specified to cause the NOTIFY to be
signed by the given key. also-notify is not meaningful for stub
zones. The default is the empty list.
check-names
This option is used to restrict the character set and syntax of
certain domain names in primary files and/or DNS responses received
from the network. The default varies according to zone type. For
primary zones the default is fail; for secondary zones the
default is warn. It is not implemented for hint zones.
This specifies the type of database to be used to store the zone data.
The string following the database keyword is interpreted as a
list of whitespace-delimited words. The first word identifies the
database type, and any subsequent words are passed as arguments to
the database to be interpreted in a way specific to the database
type.
The default is rbt, BIND 9’s native in-memory red-black tree
database. This database does not take arguments.
Other values are possible if additional database drivers have been
linked into the server. Some sample drivers are included with the
distribution but none are linked in by default.
This sets the zone’s filename. In primary, hint, and redirect
zones which do not have primaries defined, zone data is loaded from
this file. In secondary, mirror, stub, and redirect zones
which do have primaries defined, zone data is retrieved from
another server and saved in this file. This option is not applicable
to other zone types.
forward
This option is only meaningful if the zone has a forwarders list. The only value
causes the lookup to fail after trying the forwarders and getting no
answer, while first allows a normal lookup to be tried.
forwarders
This is used to override the list of global forwarders. If it is not
specified in a zone of type forward, no forwarding is done for
the zone and the global options are not used.
journal
This allows the default journal’s filename to be overridden. The default is
the zone’s filename with “.jnl” appended. This is applicable to
primary and secondary zones.
This option is only meaningful for static-stub zones. This is a list of IP addresses
to which queries should be sent in recursive resolution for the zone.
A non-empty list for this option internally configures the apex
NS RR with associated glue A or AAAA RRs.
For example, if “example.com” is configured as a static-stub zone
with 192.0.2.1 and 2001:db8::1234 in a server-addresses option,
the following RRs are internally configured:
These records are used internally to resolve names under the
static-stub zone. For instance, if the server receives a query for
“www.example.com” with the RD bit on, the server initiates
recursive resolution and sends queries to 192.0.2.1 and/or
2001:db8::1234.
server-names
This option is only meaningful for static-stub zones. This is a list of domain names
of name servers that act as authoritative servers of the static-stub
zone. These names are resolved to IP addresses when named
needs to send queries to these servers. For this supplemental
resolution to be successful, these names must not be a subdomain of the
origin name of the static-stub zone. That is, when “example.net” is the
origin of a static-stub zone, “ns.example” and “master.example.com”
can be specified in the server-names option, but “ns.example.net”
cannot; it is rejected by the configuration parser.
A non-empty list for this option internally configures the apex
NS RR with the specified names. For example, if “example.com” is
configured as a static-stub zone with “ns1.example.net” and
“ns2.example.net” in a server-names option, the following RRs
are internally configured:
These records are used internally to resolve names under the
static-stub zone. For instance, if the server receives a query for
“www.example.com” with the RD bit on, the server initiates recursive
resolution, resolves “ns1.example.net” and/or “ns2.example.net” to IP
addresses, and then sends queries to one or more of these addresses.
sig-validity-interval
See the description of sig-validity-interval in Tuning.
sig-signing-nodes
See the description of sig-signing-nodes in Tuning.
sig-signing-signatures
See the description of sig-signing-signatures in
Tuning.
sig-signing-type
See the description of sig-signing-type in Tuning.
transfer-source
See the description of transfer-source in Zone Transfers.
transfer-source-v6
See the description of transfer-source-v6 in Zone Transfers.
alt-transfer-source
See the description of alt-transfer-source in Zone Transfers.
alt-transfer-source-v6
See the description of alt-transfer-source-v6 in Zone Transfers.
use-alt-transfer-source
See the description of use-alt-transfer-source in Zone Transfers.
See the description of ixfr-from-differences in Boolean Options.
(Note that the ixfr-from-differences choices of primary and secondary
are not available at the zone level.)
If yes, BIND 9 maintains a separate signed version of the zone.
An unsigned zone is transferred in or loaded from disk and the signed
version of the zone is served with, possibly, a different serial
number. The signed version of the zone is stored in a file that is
the zone’s filename (set in file) with a .signed extension.
This behavior is disabled by default.
BIND 9 supports two methods of granting clients the right to
perform dynamic updates to a zone:
allow-update - a simple access control list
update-policy - fine-grained access control
In both cases, BIND 9 writes the updates to the zone’s filename
set in file.
In the case of a DNSSEC zone, DNSSEC records are also written to
the zone’s filename, unless inline-signing is enabled.
Note
The zone file can no longer be manually updated while named
is running; it is now necessary to perform rndcfreeze, edit,
and then perform rndcthaw. Comments and formatting
in the zone file are lost when dynamic updates occur.
The allow-update clause is a simple access control list. Any client
that matches the ACL is granted permission to update any record in the
zone.
The update-policy clause allows more fine-grained control over which
updates are allowed. It specifies a set of rules, in which each rule
either grants or denies permission for one or more names in the zone to
be updated by one or more identities. Identity is determined by the key
that signed the update request, using either TSIG or SIG(0). In most
cases, update-policy rules only apply to key-based identities. There
is no way to specify update permissions based on the client source address.
update-policy rules are only meaningful for zones of type
primary, and are not allowed in any other zone type. It is a
configuration error to specify both allow-update and
update-policy at the same time.
A pre-defined update-policy rule can be switched on with the command
update-policylocal;. named automatically
generates a TSIG session key when starting and stores it in a file;
this key can then be used by local clients to update the zone while
named is running. By default, the session key is stored in the file
/var/run/named/session.key, the key name is “local-ddns”, and the
key algorithm is HMAC-SHA256. These values are configurable with the
session-keyfile, session-keyname, and session-keyalg options,
respectively. A client running on the local system, if run with
appropriate permissions, may read the session key from the key file and
use it to sign update requests. The zone’s update policy is set to
allow that key to change any record within the zone. Assuming the key
name is “local-ddns”, this policy is equivalent to:
update-policy{grantlocal-ddnszonesubany;};
with the additional restriction that only clients connecting from the
local system are permitted to send updates.
Note that only one session key is generated by named; all zones
configured to use update-policylocal accept the same key.
The command nsupdate-l implements this feature, sending requests to
localhost and signing them using the key retrieved from the session key
file.
Other rule definitions look like this:
(grant|deny)identityruletypenametypes
Each rule grants or denies privileges. Rules are checked in the order in
which they are specified in the update-policy statement. Once a
message has successfully matched a rule, the operation is immediately
granted or denied, and no further rules are examined. There are 13 types
of rules; the rule type is specified by the ruletype field, and the
interpretation of other fields varies depending on the rule type.
In general, a rule is matched when the key that signed an update request
matches the identity field, the name of the record to be updated
matches the name field (in the manner specified by the ruletype
field), and the type of the record to be updated matches the types
field. Details for each rule type are described below.
The identity field must be set to a fully qualified domain name. In
most cases, this represents the name of the TSIG or SIG(0) key that
must be used to sign the update request. If the specified name is a
wildcard, it is subject to DNS wildcard expansion, and the rule may
apply to multiple identities. When a TKEY exchange has been used to
create a shared secret, the identity of the key used to authenticate the
TKEY exchange is used as the identity of the shared secret. Some
rule types use identities matching the client’s Kerberos principal (e.g,
"host/machine@REALM") or Windows realm (machine$@REALM).
The name field also specifies a fully qualified domain name. This often
represents the name of the record to be updated. Interpretation of this
field is dependent on rule type.
If no types are explicitly specified, then a rule matches all types
except RRSIG, NS, SOA, NSEC, and NSEC3. Types may be specified by name,
including ANY; ANY matches all types except NSEC and NSEC3, which can
never be updated. Note that when an attempt is made to delete all
records associated with a name, the rules are checked for each existing
record type.
The ruletype field has 16 values: name, subdomain, zonesub, wildcard,
self, selfsub, selfwild, ms-self, ms-selfsub, ms-subdomain,
krb5-self, krb5-selfsub, krb5-subdomain,
tcp-self, 6to4-self, and external.
name
With exact-match semantics, this rule matches when the name being updated is identical to the contents of the name field.
subdomain
This rule matches when the name being updated is a subdomain of, or identical to, the contents of the name field.
zonesub
This rule is similar to subdomain, except that it matches when the name being updated is a subdomain of the zone in which the update-policy statement appears. This obviates the need to type the zone name twice, and enables the use of a standard update-policy statement in multiple zones without modification.
When this rule is used, the name field is omitted.
wildcard
The name field is subject to DNS wildcard expansion, and this rule matches when the name being updated is a valid expansion of the wildcard.
self
This rule matches when the name of the record being updated matches the contents of the identity field. The name field is ignored. To avoid confusion, it is recommended that this field be set to the same value as the identity field or to “.”
The self rule type is most useful when allowing one key per name to update, where the key has the same name as the record to be updated. In this case, the identity field can be specified as * (asterisk).
selfsub
This rule is similar to self, except that subdomains of self can also be updated.
selfwild
This rule is similar to self, except that only subdomains of self can be updated.
ms-self
When a client sends an UPDATE using a Windows machine principal (for example, machine$@REALM), this rule allows records with the absolute name of machine.REALM to be updated.
The realm to be matched is specified in the identity field.
The name field has no effect on this rule; it should be set to “.” as a placeholder.
For example, grantEXAMPLE.COMms-self.AAAAA allows any machine with a valid principal in the realm EXAMPLE.COM to update its own address records.
ms-selfsub
This is similar to ms-self, except it also allows updates to any subdomain of the name specified in the Windows machine principal, not just to the name itself.
ms-subdomain
When a client sends an UPDATE using a Windows machine principal (for example, machine$@REALM), this rule allows any machine in the specified realm to update any record in the zone or in a specified subdomain of the zone.
The realm to be matched is specified in the identity field.
The name field specifies the subdomain that may be updated. If set to “.” or any other name at or above the zone apex, any name in the zone can be updated.
For example, if update-policy for the zone “example.com” includes grantEXAMPLE.COMms-subdomainhosts.example.com.AAAAAA, any machine with a valid principal in the realm EXAMPLE.COM is able to update address records at or below hosts.example.com.
krb5-self
When a client sends an UPDATE using a Kerberos machine principal (for example, host/machine@REALM), this rule allows records with the absolute name of machine to be updated, provided it has been authenticated by REALM. This is similar but not identical to ms-self, due to the machine part of the Kerberos principal being an absolute name instead of an unqualified name.
The realm to be matched is specified in the identity field.
The name field has no effect on this rule; it should be set to “.” as a placeholder.
For example, grantEXAMPLE.COMkrb5-self.AAAAA allows any machine with a valid principal in the realm EXAMPLE.COM to update its own address records.
krb5-selfsub
This is similar to krb5-self, except it also allows updates to any subdomain of the name specified in the machine part of the Kerberos principal, not just to the name itself.
krb5-subdomain
This rule is identical to ms-subdomain, except that it works with Kerberos machine principals (i.e., host/machine@REALM) rather than Windows machine principals.
tcp-self
This rule allows updates that have been sent via TCP and for which the standard mapping from the client’s IP address into the in-addr.arpa and ip6.arpa namespaces matches the name to be updated. The identity field must match that name. The name field should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.
Note
It is theoretically possible to spoof these TCP sessions.
6to4-self
This allows the name matching a 6to4 IPv6 prefix, as specified in RFC 3056, to be updated by any TCP connection from either the 6to4 network or from the corresponding IPv4 address. This is intended to allow NS or DNAME RRsets to be added to the ip6.arpa reverse tree.
The identity field must match the 6to4 prefix in ip6.arpa. The name field should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.
In addition, if specified for an ip6.arpa name outside of the 2.0.0.2.ip6.arpa namespace, the corresponding /48 reverse name can be updated. For example, TCP/IPv6 connections from 2001:DB8:ED0C::/48 can update records at C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa.
Note
It is theoretically possible to spoof these TCP sessions.
external
This rule allows named to defer the decision of whether to allow a given update to an external daemon.
The method of communicating with the daemon is specified in the identity field, the format of which is “local:path”, where “path” is the location of a Unix-domain socket. (Currently, “local” is the only supported mechanism.)
Requests to the external daemon are sent over the Unix-domain socket as datagrams with the following format:
The daemon replies with a four-byte value in network byte order, containing either 0 or 1; 0 indicates that the specified update is not permitted, and 1 indicates that it is.
Warning
The external daemon must not delay communication. This policy is evaluated synchronously; any wait period negatively affects named performance.
When multiple views are in use, a zone may be referenced by more than
one of them. Often, the views contain different zones with the same
name, allowing different clients to receive different answers for the
same queries. At times, however, it is desirable for multiple views to
contain identical zones. The in-view zone option provides an
efficient way to do this; it allows a view to reference a zone that was
defined in a previously configured view. For example:
An in-view option cannot refer to a view that is configured later in
the configuration file.
A zone statement which uses the in-view option may not use any
other options, with the exception of forward and forwarders.
(These options control the behavior of the containing view, rather than
change the zone object itself.)
Zone-level ACLs (e.g., allow-query, allow-transfer), and other
configuration details of the zone, are all set in the view the referenced
zone is defined in. Be careful to ensure that ACLs are wide
enough for all views referencing the zone.
An in-view zone cannot be used as a response policy zone.
An in-view zone is not intended to reference a forward zone.
This section, largely borrowed from RFC 1034, describes the concept of a
Resource Record (RR) and explains when each type is used. Since the
publication of RFC 1034, several new RRs have been identified and
implemented in the DNS. These are also included.
A domain name identifies a node. Each node has a set of resource
information, which may be empty. The set of resource information
associated with a particular name is composed of separate RRs. The order
of RRs in a set is not significant and need not be preserved by name
servers, resolvers, or other parts of the DNS. However, sorting of
multiple RRs is permitted for optimization purposes: for example, to
specify that a particular nearby server be tried first. See
The sortlist Statement and RRset Ordering.
The components of a Resource Record are:
owner name
The domain name where the RR is found.
type
An encoded 16-bit value that specifies the type of the resource record.
TTL
The time-to-live of the RR. This field is a 32-bit integer in units of seconds, and is primarily used by resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded.
class
An encoded 16-bit value that identifies a protocol family or an instance of a protocol.
RDATA
The resource data. The format of the data is type- and sometimes class-specific.
The following classes of resource records are currently valid in the
DNS:
IN
The Internet.
CH
Chaosnet, a LAN protocol created at MIT in the mid-1970s. It was rarely used for its historical purpose, but was reused for BIND’s built-in server information zones, e.g., version.bind.
HS
Hesiod, an information service developed by MIT’s Project Athena. It was used to share information about various systems databases, such as users, groups, printers, etc.
The owner name is often implicit, rather than forming an integral part
of the RR. For example, many name servers internally form tree or hash
structures for the name space, and chain RRs off nodes. The remaining RR
parts are the fixed header (type, class, TTL), which is consistent for
all RRs, and a variable part (RDATA) that fits the needs of the resource
being described.
The TTL field is a time limit on how long an RR can be
kept in a cache. This limit does not apply to authoritative data in
zones; that also times out, but follows the refreshing policies for the
zone. The TTL is assigned by the administrator for the zone where the
data originates. While short TTLs can be used to minimize caching, and a
zero TTL prohibits caching, the realities of Internet performance
suggest that these times should be on the order of days for the typical
host. If a change is anticipated, the TTL can be reduced prior to
the change to minimize inconsistency, and then
increased back to its former value following the change.
The data in the RDATA section of RRs is carried as a combination of
binary strings and domain names. The domain names are frequently used as
“pointers” to other data in the DNS.
RRs are represented in binary form in the packets of the DNS protocol,
and are usually represented in highly encoded form when stored in a name
server or resolver. In the examples provided in RFC 1034, a style
similar to that used in primary files was employed in order to show the
contents of RRs. In this format, most RRs are shown on a single line,
although continuation lines are possible using parentheses.
The start of the line gives the owner of the RR. If a line begins with a
blank, then the owner is assumed to be the same as that of the previous
RR. Blank lines are often included for readability.
Following the owner are listed the TTL, type, and class of the RR. Class
and type use the mnemonics defined above, and TTL is an integer before
the type field. To avoid ambiguity in parsing, type and class
mnemonics are disjoint, TTLs are integers, and the type mnemonic is
always last. The IN class and TTL values are often omitted from examples
in the interest of clarity.
The resource data or RDATA section of the RR is given using knowledge
of the typical representation for the data.
For example, the RRs carried in a message might be shown as:
ISI.EDU.
MX
10VENERA.ISI.EDU.
MX
10VAXA.ISI.EDU
VENERA.ISI.EDU
A
128.9.0.32
A
10.1.0.52
VAXA.ISI.EDU
A
10.2.0.27
A
128.9.0.33
The MX RRs have an RDATA section which consists of a 16-bit number
followed by a domain name. The address RRs use a standard IP address
format to contain a 32-bit Internet address.
The above example shows six RRs, with two RRs at each of three domain
names.
Here is another possible example:
XX.LCS.MIT.EDU.
INA
10.0.0.44
CHA
MIT.EDU.2420
This shows two addresses for XX.LCS.MIT.EDU, each of a
different class.
As described above, domain servers store information as a series of
resource records, each of which contains a particular piece of
information about a given domain name (which is usually, but not always,
a host). The simplest way to think of an RR is as a typed pair of data, a
domain name matched with a relevant datum and stored with some
additional type information, to help systems determine when the RR is
relevant.
MX records are used to control delivery of email. The data specified in
the record is a priority and a domain name. The priority controls the
order in which email delivery is attempted, with the lowest number
first. If two priorities are the same, a server is chosen randomly. If
no servers at a given priority are responding, the mail transport agent
falls back to the next largest priority. Priority numbers do not
have any absolute meaning; they are relevant only respective to other
MX records for that domain name. The domain name given is the machine to
which the mail is delivered. It must have an associated address
record (A or AAAA); CNAME is not sufficient.
For a given domain, if there is both a CNAME record and an MX record,
the MX record is in error and is ignored. Instead, the mail is
delivered to the server specified in the MX record pointed to by the
CNAME. For example:
example.com.
IN
MX
10
mail.example.com.
IN
MX
10
mail2.example.com.
IN
MX
20
mail.backup.org.
mail.example.com.
IN
A
10.0.0.1
mail2.example.com.
IN
A
10.0.0.2
Mail delivery is attempted to mail.example.com and
mail2.example.com (in any order); if neither of those succeeds,
delivery to mail.backup.org is attempted.
The time-to-live (TTL) of the RR field is a 32-bit integer represented in
units of seconds, and is primarily used by resolvers when they cache
RRs. The TTL describes how long an RR can be cached before it should be
discarded. The following three types of TTLs are currently used in a zone
file.
SOA
The last field in the SOA is the negative caching TTL. This controls how long other servers cache no-such-domain (NXDOMAIN) responses from this server.
The maximum time for negative caching is 3 hours (3h).
$TTL
The $TTL directive at the top of the zone file (before the SOA) gives a default TTL for every RR without a specific TTL set.
RR TTLs
Each RR can have a TTL as the second field in the RR, which controls how long other servers can cache it.
All of these TTLs default to units of seconds, though units can be
explicitly specified: for example, 1h30m.
Reverse name resolution (that is, translation from IP address to name)
is achieved by means of the in-addr.arpa domain and PTR records.
Entries in the in-addr.arpa domain are made in least-to-most significant
order, read left to right. This is the opposite order to the way IP
addresses are usually written. Thus, a machine with an IP address of
10.1.2.3 would have a corresponding in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose
data field is the name of the machine or, optionally, multiple PTR
records if the machine has more than one name. For example, in the
example.com domain:
$ORIGIN
2.1.10.in-addr.arpa
3
INPTRfoo.example.com.
Note
The $ORIGIN line in this example is only to provide context;
it does not necessarily appear in the actual
usage. It is only used here to indicate that the example is
relative to the listed origin.
The DNS “master file” format was initially defined in RFC 1035 and has
subsequently been extended. While the format itself is class-independent,
all records in a zone file must be of the same class.
Master file directives include $ORIGIN, $INCLUDE, and $TTL.
When used in the label (or name) field, the asperand or at-sign (@)
symbol represents the current origin. At the start of the zone file, it
is the <zone_name>, followed by a trailing dot (.).
$ORIGIN sets the domain name that is appended to any
unqualified records. When a zone is first read, there is an implicit
$ORIGIN <zone_name>``.``; note the trailing dot. The
current $ORIGIN is appended to the domain specified in the
$ORIGIN argument if it is not absolute.
This reads and processes the file filename as if it were included in the
file at this point. The filename can be an absolute path, or a relative
path. In the latter case it is read from named’s working directory. If
origin is specified, the file is processed with $ORIGIN set to that
value; otherwise, the current $ORIGIN is used.
The origin and the current domain name revert to the values they had
prior to the $INCLUDE once the file has been read.
Note
RFC 1035 specifies that the current origin should be restored after
an $INCLUDE, but it is silent on whether the current domain name
should also be restored. BIND 9 restores both of them. This could be
construed as a deviation from RFC 1035, a feature, or both.
BIND Primary File Extension: the $GENERATE Directive
Syntax: $GENERATE range owner [ttl] [class] type rdata [comment]
$GENERATE is used to create a series of resource records that only
differ from each other by an iterator.
range
This can be one of two forms: start-stop or start-stop/step.
If the first form is used, then step is set to 1. “start”,
“stop”, and “step” must be positive integers between 0 and
(2^31)-1. “start” must not be larger than “stop”.
owner
This describes the owner name of the resource records to be created.
The owner string may include one or more $ (dollar sign)
symbols, which will be replaced with the iterator value when
generating records; see below for details.
ttl
This specifies the time-to-live of the generated records. If
not specified, this is inherited using the normal TTL inheritance
rules.
class and ttl can be entered in either order.
class
This specifies the class of the generated records. This must
match the zone class if it is specified.
class and ttl can be entered in either order.
type
This can be any valid type.
rdata
This is a string containing the RDATA of the resource record
to be created. As with owner, the rdata string may
include one or more $ symbols, which are replaced with the
iterator value. rdata may be quoted if there are spaces in
the string; the quotation marks do not appear in the generated
record.
Any single $ (dollar sign) symbols within the owner or
rdata strings are replaced by the iterator value. To get a $
in the output, escape the $ using a backslash \\, e.g.,
\$. (For compatibility with earlier versions, $$ is also
recognized as indicating a literal $ in the output.)
The $ may optionally be followed by modifiers which change
the offset from the iterator, field width, and base. Modifiers
are introduced by a { (left brace) immediately following
the $, as in ${offset[,width[,base]]}. For example,
${-20,3,d} subtracts 20 from the current value and prints
the result as a decimal in a zero-padded field of width 3.
Available output forms are decimal (d), octal (o),
hexadecimal (x or X for uppercase), and nibble (n
or N for uppercase). The modfiier cannot contain whitespace
or newlines.
The default modifier is ${0,0,d}. If the owner is not
absolute, the current $ORIGIN is appended to the name.
In nibble mode, the value is treated as if it were a reversed
hexadecimal string, with each hexadecimal digit as a separate
label. The width field includes the label separator.
Examples:
$GENERATE can be used to easily generate the sets of records required
to support sub-/24 reverse delegations described in RFC 2317:
In addition to the standard text format, BIND 9 supports the ability
to read or dump to zone files in other formats.
The raw format is a binary representation of zone data in a manner
similar to that used in zone transfers. Since it does not require
parsing text, load time is significantly reduced.
An even faster alternative is the map format, which is an image of a
BIND 9 in-memory zone database; it can be loaded directly into memory via
the mmap() function and the zone can begin serving queries almost
immediately. Because records are not indivdually processed when loading a
map file, zones using this format cannot be used in response-policy
statements.
For a primary server, a zone file in raw or map format is expected
to be generated from a text zone file by the named-compilezone command.
For a secondary server or a dynamic zone, the zone file is automatically
generated when named dumps the zone contents after zone transfer or
when applying prior updates, if one of these formats is specified by the
masterfile-format option.
If a zone file in a binary format needs manual modification, it first must
be converted to text format by the named-compilezone command,
then converted back after editing. For example:
::
named-compilezone -f map -F text -o zonefile.text <origin> zonefile.map
[edit zonefile.text]
named-compilezone -f text -F map -o zonefile.map <origin> zonefile.text
Note that the map format is highly architecture-specific. A map
file cannot be used on a system with different pointer size, endianness,
or data alignment than the system on which it was generated, and should in
general be used only inside a single system.
The map format is also dependent on the internal memory representation
of a zone database, which may change from one release of BIND 9 to another.
map files are never compatible across major releases, and may not be
compatible across minor releases; any upgrade to BIND 9 may cause map
files to be rejected when loading. If a map file is being used for a
primary zone, it will need to be regenerated from text before restarting
the server. If it used for a secondary zone, this is unnecessary; the
rejection of the file will trigger a retransfer of the zone from the
primary. (To avoid a spike in traffic upon restart, it may be desirable in
some cases to convert map files to text format using
named-compilezone before an upgrade, then back to map format with
the new version of named-compilezone afterward.)
The use of map format may also be limited by operating system
mmap(2) limits like sysctlvm.max_map_count. For Linux, this
defaults to 65536, which limits the number of mapped zones that can
be used without increasing vm.max_map_count.
raw format uses network byte order and avoids architecture-
dependent data alignment so that it is as portable as possible, but it is
still primarily expected to be used inside the same single system. To
export a zone file in either raw or map format, or make a portable
backup of such a file, conversion to text format is recommended.
BIND 9 maintains lots of statistics information and provides several
interfaces for users to access those statistics. The available
statistics include all statistics counters that are meaningful in BIND 9,
and other information that is considered useful.
The statistics information is categorized into the following sections:
Incoming Requests
The number of incoming DNS requests for each OPCODE.
Incoming Queries
The number of incoming queries for each RR type.
Outgoing Queries
The number of outgoing queries for each RR type sent from the internal
resolver, maintained per view.
Name Server Statistics
Statistics counters for incoming request processing.
Zone Maintenance Statistics
Statistics counters regarding zone maintenance operations, such as zone
transfers.
Resolver Statistics
Statistics counters for name resolutions performed in the internal resolver,
maintained per view.
Cache DB RRsets
Statistics counters related to cache contents, maintained per view.
The “NXDOMAIN” counter is the number of names that have been cached as
nonexistent. Counters named for RR types indicate the number of active
RRsets for each type in the cache database.
If an RR type name is preceded by an exclamation point (!), it represents the
number of records in the cache which indicate that the type does not exist
for a particular name; this is also known as “NXRRSET”. If an RR type name
is preceded by a hash mark (#), it represents the number of RRsets for this
type that are present in the cache but whose TTLs have expired; these RRsets
may only be used if stale answers are enabled. If an RR type name is
preceded by a tilde (~), it represents the number of RRsets for this type
that are present in the cache database but are marked for garbage collection;
these RRsets cannot be used.
Socket I/O Statistics
Statistics counters for network-related events.
A subset of Name Server Statistics is collected and shown per zone for
which the server has the authority, when zone-statistics is set to
full (or yes), for backward compatibility. See the description of
zone-statistics in options Statement Definition and Usage for further details.
These statistics counters are shown with their zone and view names. The
view name is omitted when the server is not configured with explicit
views.
There are currently two user interfaces to get access to the statistics.
One is in plain-text format, dumped to the file specified by the
statistics-file configuration option; the other is remotely
accessible via a statistics channel when the statistics-channels
statement is specified in the configuration file (see statistics-channels Statement Grammar.)
The text format statistics dump begins with a line, like:
+++StatisticsDump+++(973798949)
The number in parentheses is a standard Unix-style timestamp, measured
in seconds since January 1, 1970. Following that line is a set of
statistics information, which is categorized as described above. Each
section begins with a line, like:
++NameServerStatistics++
Each section consists of lines, each containing the statistics counter
value followed by its textual description; see below for available
counters. For brevity, counters that have a value of 0 are not shown in
the statistics file.
The statistics dump ends with the line where the number is identical to
the number in the beginning line; for example:
The following lists summarize the statistics counters that BIND 9 provides.
For each counter, the abbreviated
symbol name is given; these symbols are shown in the statistics
information accessed via an HTTP statistics channel.
The description of the counter is also shown in the
statistics file but, in this document, may be slightly
modified for better readability.
This indicates the number of IPv4 requests received. Note: this also counts non-query requests.
Requestv6
This indicates the number of IPv6 requests received. Note: this also counts non-query requests.
ReqEdns0
This indicates the number of requests received with EDNS(0).
ReqBadEDNSVer
This indicates the number of requests received with an unsupported EDNS version.
ReqTSIG
This indicates the number of requests received with TSIG.
ReqSIG0
This indicates the number of requests received with SIG(0).
ReqBadSIG
This indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.
ReqTCP
This indicates the number of TCP requests received.
AuthQryRej
This indicates the number of rejected authoritative (non-recursive) queries.
RecQryRej
This indicates the number of rejected recursive queries.
XfrRej
This indicates the number of rejected zone transfer requests.
UpdateRej
This indicates the number of rejected dynamic update requests.
Response
This indicates the number of responses sent.
RespTruncated
This indicates the number of truncated responses sent.
RespEDNS0
This indicates the number of responses sent with EDNS(0).
RespTSIG
This indicates the number of responses sent with TSIG.
RespSIG0
This indicates the number of responses sent with SIG(0).
QrySuccess
This indicates the number of queries that resulted in a successful answer, meaning queries which return a NOERROR response with at least one answer RR. This corresponds to the success counter of previous versions of BIND 9.
QryAuthAns
This indicates the number of queries that resulted in an authoritative answer.
QryNoauthAns
This indicates the number of queries that resulted in a non-authoritative answer.
QryReferral
This indicates the number of queries that resulted in a referral answer. This corresponds to the referral counter of previous versions of BIND 9.
QryNxrrset
This indicates the number of queries that resulted in NOERROR responses with no data. This corresponds to the nxrrset counter of previous versions of BIND 9.
QrySERVFAIL
This indicates the number of queries that resulted in SERVFAIL.
QryFORMERR
This indicates the number of queries that resulted in FORMERR.
QryNXDOMAIN
This indicates the number of queries that resulted in NXDOMAIN. This corresponds to the nxdomain counter of previous versions of BIND 9.
QryRecursion
This indicates the number of queries that caused the server to perform recursion in order to find the final answer. This corresponds to the recursion counter of previous versions of BIND 9.
QryDuplicate
This indicates the number of queries which the server attempted to recurse but for which it discovered an existing query with the same IP address, port, query ID, name, type, and class already being processed. This corresponds to the duplicate counter of previous versions of BIND 9.
QryDropped
This indicates the number of recursive queries for which the server discovered an excessive number of existing recursive queries for the same name, type, and class, and which were subsequently dropped. This is the number of dropped queries due to the reason explained with the clients-per-query and max-clients-per-query options (see clients-per-query). This corresponds to the dropped counter of previous versions of BIND 9.
QryFailure
This indicates the number of query failures. This corresponds to the failure counter of previous versions of BIND 9. Note: this counter is provided mainly for backward compatibility with previous versions; normally, more fine-grained counters such as AuthQryRej and RecQryRej that would also fall into this counter are provided, so this counter is not of much interest in practice.
QryNXRedir
This indicates the number of queries that resulted in NXDOMAIN that were redirected.
QryNXRedirRLookup
This indicates the number of queries that resulted in NXDOMAIN that were redirected and resulted in a successful remote lookup.
XfrReqDone
This indicates the number of requested and completed zone transfers.
UpdateReqFwd
This indicates the number of forwarded update requests.
UpdateRespFwd
This indicates the number of forwarded update responses.
UpdateFwdFail
This indicates the number of forwarded dynamic updates that failed.
UpdateDone
This indicates the number of completed dynamic updates.
UpdateFail
This indicates the number of failed dynamic updates.
UpdateBadPrereq
This indicates the number of dynamic updates rejected due to a prerequisite failure.
UpdateQuota
This indicates the number of times a dynamic update or update
forwarding request was rejected because the number of pending
requests exceeded update-quota.
RateDropped
This indicates the number of responses dropped due to rate limits.
RateSlipped
This indicates the number of responses truncated by rate limits.
RPZRewrites
This indicates the number of response policy zone rewrites.
This indicates the number of IPv4 responses received.
Responsev6
This indicates the number of IPv6 responses received.
NXDOMAIN
This indicates the number of NXDOMAINs received.
SERVFAIL
This indicates the number of SERVFAILs received.
FORMERR
This indicates the number of FORMERRs received.
OtherError
This indicates the number of other errors received.
EDNS0Fail
This indicates the number of EDNS(0) query failures.
Mismatch
This indicates the number of mismatched responses received, meaning the DNS ID, response’s source address, and/or the response’s source port does not match what was expected. (The port must be 53 or as defined by the port option.) This may be an indication of a cache poisoning attempt.
Truncated
This indicates the number of truncated responses received.
Lame
This indicates the number of lame delegations received.
Retry
This indicates the number of query retries performed.
QueryAbort
This indicates the number of queries aborted due to quota control.
QuerySockFail
This indicates the number of failures in opening query sockets. One common reason for such failures is due to a limitation on file descriptors.
QueryTimeout
This indicates the number of query timeouts.
GlueFetchv4
This indicates the number of IPv4 NS address fetches invoked.
GlueFetchv6
This indicates the number of IPv6 NS address fetches invoked.
GlueFetchv4Fail
This indicates the number of failed IPv4 NS address fetches.
GlueFetchv6Fail
This indicates the number of failed IPv6 NS address fetches.
ValAttempt
This indicates the number of attempted DNSSEC validations.
ValOk
This indicates the number of successful DNSSEC validations.
ValNegOk
This indicates the number of successful DNSSEC validations on negative information.
ValFail
This indicates the number of failed DNSSEC validations.
QryRTTnn
This provides a frequency table on query round-trip times (RTTs). Each nn specifies the corresponding frequency. In the sequence of nn_1, nn_2, …, nn_m, the value of nn_i is the number of queries whose RTTs are between nn_(i-1) (inclusive) and nn_i (exclusive) milliseconds. For the sake of convenience, we define nn_0 to be 0. The last entry should be represented as nn_m+, which means the number of queries whose RTTs are equal to or greater than nn_m milliseconds.
Socket I/O statistics counters are defined per socket type, which are
UDP4 (UDP/IPv4), UDP6 (UDP/IPv6), TCP4 (TCP/IPv4), TCP6
(TCP/IPv6), Unix (Unix Domain), and FDwatch (sockets opened
outside the socket module). In the following list, <TYPE> represents
a socket type. Not all counters are available for all socket types;
exceptions are noted in the descriptions.
<TYPE>Open
This indicates the number of sockets opened successfully. This counter does not apply to the FDwatch type.
<TYPE>OpenFail
This indicates the number of failures to open sockets. This counter does not apply to the FDwatch type.
<TYPE>Close
This indicates the number of closed sockets.
<TYPE>BindFail
This indicates the number of failures to bind sockets.
<TYPE>ConnFail
This indicates the number of failures to connect sockets.
<TYPE>Conn
This indicates the number of connections established successfully.
<TYPE>AcceptFail
This indicates the number of failures to accept incoming connection requests. This counter does not apply to the UDP and FDwatch types.
<TYPE>Accept
This indicates the number of incoming connections successfully accepted. This counter does not apply to the UDP and FDwatch types.
<TYPE>SendErr
This indicates the number of errors in socket send operations.
<TYPE>RecvErr
This indicates the number of errors in socket receive operations, including errors of send operations on a connected UDP socket, notified by an ICMP error message.
DNS Security Extensions (DNSSEC) provide reliable protection from
cache poisoning attacks. At the same time these extensions also provide other benefits:
they limit the impact of random subdomain attacks on resolver caches and authoritative
servers, and provide the foundation for modern applications like authenticated
and private e-mail transfer.
To achieve this goal, DNSSEC adds digital signatures to DNS records in
authoritative DNS zones, and DNS resolvers verify the validity of the signatures on the
received records. If the signatures match the received data, the resolver can
be sure that the data was not modified in transit.
Note
DNSSEC and transport-level encryption are complementary!
Unlike typical transport-level encryption like DNS-over-TLS, DNS-over-HTTPS,
or VPN, DNSSEC makes DNS records verifiable at all points of the DNS
resolution chain.
Regardless of the zone-signing method in use, cryptographic keys are
stored in files named like Kdnssec.example.+013+12345.key and
Kdnssec.example.+013+12345.private.
The private key (in the .private file) is used to generate signatures, and
the public key (in the .key file) is used for signature verification.
Additionally, the Fully Automated (Key and Signing Policy) method creates a third file,
Kdnssec.example+013+12345.state, which is used to track DNSSEC key timings
and to perform key rollovers safely.
These filenames contain:
the key name, which always matches the zone name (dnssec.example.),
the algorithm number (013 is ECDSAP256SHA256, 008 is RSASHA256, etc.),
and the key tag, i.e. a non-unique key identifier (12345 in this case).
Warning
Private keys are required for full disaster recovery. Back up key files in a
safe location and protect them from unauthorized access. Anyone with
access to the private key can create fake but seemingly valid DNS data.
Key and Signing Policy (KASP) is a method of configuration that describes
how to maintain DNSSEC signing keys and how to sign the zone.
This is the recommended, fully automated way to sign and maintain DNS zones. For
most use cases users can simply use the built-in default policy, which applies
up-to-date DNSSEC practices:
zone "dnssec.example" {
type primary;
file "dnssec.example.db";
dnssec-policy default;
inline-signing yes;
};
The dnssec-policy statement requires dynamic DNS to be set up, or
inline-signing to be enabled. In the example above we use the latter.
This is sufficient to create the necessary signing keys, and generate
DNSKEY, RRSIG, and NSEC records for the zone. BIND also takes
care of any DNSSEC maintenance for this zone, including replacing signatures
that are about to expire and managing Key Rollovers.
The default policy creates one key that is used to sign the complete zone,
and uses NSEC to enable authenticated denial of existence (a secure way
to tell which records do not exist in a zone). This policy is recommended
and typically does not need to be changed.
If needed, a custom policy can be defined by adding a dnssec-policy statement
into the configuration:
uses two keys to sign the zone: a Key Signing Key (KSK) to sign the key
related RRsets (DNSKEY, CDS, and CDNSKEY), and a Zone Signing
Key (ZSK) to sign the rest of the zone. The KSK is automatically
rotated after one year and the ZSK after 60 days.
Also:
The configured keys have a lifetime set and use the ECDSAP384SHA384
algorithm.
The last line instructs BIND to generate NSEC3 records for
Proof of Non-Existence,
using zero extra iterations and no salt. NSEC3 opt-out is disabled, meaning
insecure delegations also get an NSEC3 record.
The Advanced Discussions section in the DNSSEC Guide discusses the
various policy settings and may be useful for determining values for specific
needs.
When using a dnssec-policy, a key lifetime can be set to trigger
key rollovers. ZSK rollovers are fully automatic, but for KSK and CSK rollovers
a DS record needs to be submitted to the parent. See
Secure Delegation for possible ways to do so.
Once the DS is in the parent (and the DS of the predecessor key is withdrawn),
BIND needs to be told that this event has happened. This can be done automatically
by configuring parental agents:
zone "dnssec.example" {
type primary;
file "dnssec.example.db";
dnssec-policy default;
inline-signing yes;
parental-agents { 192.0.2.1; };
};
Here one server, 192.0.2.1, is configured for BIND to send DS queries to,
to check the DS RRset for dnssec-example during key rollovers. This needs
to be a trusted server, because BIND does not validate the response.
If setting up a parental agent is undesirable, it is also possible to tell BIND that the
DS is published in the parent with:
rndcdnssec-checkds-key12345publisheddnssec.example.<rndcdnssec>.
and the DS for the predecessor key has been removed with:
rndcdnssec-checkds-key54321withdrawndnssec.example.<rndcdnssec>.
where 12345 and 54321 are the key tags of the successor and predecessor key,
respectively.
To roll a key sooner than scheduled, or to roll a key that
has an unlimited lifetime, use:
rndcdnssec-rollover-key12345dnssec.example.<rndcdnssec>.
To revert a signed zone back to an insecure zone, change
the zone configuration to use the built-in “insecure” policy. Detailed
instructions are described in Reverting to Unsigned.
The method described here allows full control over the keys used to sign
the zone. This is required only for very special cases and is generally
discouraged. Under normal circumstances, please use Fully Automated (Key and Signing Policy).
Dynamic zones provide the ability to sign a zone by multiple providers, meaning
each provider signs and serves the same zone independently. Such a setup requires
some coordination between providers when it comes to key rollovers, and may be
better suited to be configured with auto-dnssecallow;. This permits keys to
be updated and the zone to be re-signed only if the user issues the command
rndcsignzonename<rndcsign>.
A zone can also be configured with auto-dnssecmaintain, which automatically
adjusts the zone’s DNSSEC keys on a schedule according to the key timing
metadata. However, keys still need to be generated separately, for
example with dnssec-keygen.
Of course, dynamic zones can also use dnssec-policy to fully automate DNSSEC
maintenance. The next sections assume that more key
management control is needed, and describe how to use dynamic DNS update to perform
various DNSSEC operations.
As an alternative to fully automated zone signing using dnssec-policy, a zone can be changed from insecure to secure using a dynamic
DNS update. named must be configured so that it can see the K*
files which contain the public and private parts of the zone keys that are
used to sign the zone. Key files should be placed in the key-directory, as
specified in named.conf:
If there are both a KSK and a ZSK available (or a CSK), this configuration causes the
zone to be signed. An NSEC chain is generated as part of the initial signing
process.
In any secure zone which supports dynamic updates, named periodically
re-signs RRsets which have not been re-signed as a result of some update action.
The signature lifetimes are adjusted to spread the re-sign load over time rather
than all at once.
To sign using NSEC3 instead of NSEC, add an NSEC3PARAM record to the initial update
request. The OPTOUT bit in the NSEC3
chain can be set in the flags field of the
NSEC3PARAM record.
Note that the NSEC3PARAM record does not show up until named has
had a chance to build/remove the relevant chain. A private type record is
created to record the state of the operation (see below for more details), and
is removed once the operation completes.
The NSEC3 chain is generated and the NSEC3PARAM record is added before
the NSEC chain is destroyed.
While the initial signing and NSEC/NSEC3 chain generation are occurring,
other updates are possible as well.
A new NSEC3PARAM record can be added via dynamic update. When the new
NSEC3 chain has been generated, the NSEC3PARAM flag field is set to
zero. At that point, the old NSEC3PARAM record can be removed. The old
chain is removed after the update request completes.
named only supports creating new NSEC3 chains where all the
NSEC3 records in the zone have the same OPTOUT state. named
supports updates to zones where the NSEC3 records in the chain have mixed
OPTOUT state. named does not support changing the OPTOUT
state of an individual NSEC3 record; if the OPTOUT state of an
individual NSEC3 needs to be changed, the entire chain must be changed.
To switch back to NSEC, use nsupdate to remove any NSEC3PARAM
records. The NSEC chain is generated before the NSEC3 chain is removed.
To perform key rollovers via a dynamic update, the K* files for the new keys
must be added so that named can find them. The new DNSKEY RRs can
then be added via dynamic update. When the zones are being signed, they are
signed with the new key set; when the signing is complete, the private type
records are updated so that the last octet is non-zero.
If this is for a KSK, the parent and any trust anchor repositories of the new
KSK must be informed.
The maximum TTL in the zone must expire before removing the old DNSKEY. If
it is a KSK that is being updated, the DS RRset in the parent must also be
updated and its TTL allowed to expire. This ensures that all clients are able to
verify at least one signature when the old DNSKEY is removed.
The old DNSKEY can be removed via UPDATE, taking care to specify the
correct key. named cleans out any signatures generated by the old
key after the update completes.
To convert a signed zone to unsigned using dynamic DNS, delete all the
DNSKEY records from the zone apex using nsupdate. All signatures,
NSEC or NSEC3 chains, and associated NSEC3PARAM records are removed
automatically when the zone is supposed to be re-signed.
This requires the dnssec-secure-to-insecure option to be set to yes in
named.conf.
In addition, if the auto-dnssecmaintain or a dnssec-policy is used, it
should be removed or changed to allow instead; otherwise it will re-sign.
There are several tools available to manually sign a zone.
Warning
Please note manual procedures are available mainly for backwards
compatibility and should be used only by expert users with specific needs.
To set up a DNSSEC secure zone manually, a series of steps
must be followed. Please see chapter
Manual Signing in the
DNSSEC Guide for more information.
The state of the signing process is signaled by private type records (with a
default type value of 65534). When signing is complete, those records with a
non-zero initial octet have a non-zero value for the final octet.
If the first octet of a private type record is non-zero, the record indicates
either that the zone needs to be signed with the key matching the record, or
that all signatures that match the record should be removed. Here are the
meanings of the different values of the first octet:
algorithm (octet 1)
key ID in network order (octet 2 and 3)
removal flag (octet 4)
complete flag (octet 5)
Only records flagged as “complete” can be removed via dynamic update; attempts
to remove other private type records are silently ignored.
If the first octet is zero (this is a reserved algorithm number that should
never appear in a DNSKEY record), the record indicates that changes to the
NSEC3 chains are in progress. The rest of the record contains an
NSEC3PARAM record, while the flag field tells what operation to perform
based on the flag bits:
Once a zone is signed on the authoritative servers, the last remaining step
is to establish chain of trust 1 between the parent zone
(example.) and the local zone (dnssec.example.).
Generally the procedure is:
Wait for stale data to expire from caches. The amount of time required
is equal to the maximum TTL value used in the zone before signing. This
step ensures that unsigned data expire from caches and resolvers do not get
confused by missing signatures.
Insert/update DS records in the parent zone (dnssec.example.DS record).
There are multiple ways to update DS records in the parent zone. Refer to the
documentation for the parent zone to find out which options are applicable to
a given case zone. Generally the options are, from most- to least-recommended:
Automatically update the DS record in the parent zone using
CDS/CDNSKEY records automatically generated by BIND. This requires
support for RFC 7344 in either parent zone, registry, or registrar. In
that case, configure BIND to monitor DS records in the parent
zone and everything will happen automatically at the right
time.
Query the zone for automatically generated CDS or CDNSKEY records using
dig, and then insert these records into the parent zone using
the method specified by the parent zone (web form, e-mail, API, …).
Generate DS records manually using the dnssec-dsfromkey utility on
zone keys, and then insert them into the parent zone.
The BIND resolver validates answers from authoritative servers by default. This
behavior is controlled by the configuration statement dnssec-validation.
By default a trust anchor for the DNS root zone is used.
This trust anchor is provided as part of BIND and is kept up-to-date using
Dynamic Trust Anchor Management.
Note
DNSSEC validation works “out of the box” and does not require
additional configuration. Additional configuration options are intended only
for special cases.
To validate answers, the resolver needs at least one trusted starting point,
a “trust anchor.” Essentially, trust anchors are copies of DNSKEY RRs for
zones that are used to form the first link in the cryptographic chain of trust.
Alternative trust anchors can be specified using trust-anchors Statement Grammar, but
this setup is very unusual and is recommended only for expert use.
For more information, see Trust Anchors in the
DNSSEC Guide.
The BIND authoritative server does not verify signatures on load, so zone keys
for authoritative zones do not need to be specified in the configuration
file.
When DNSSEC validation is configured, the resolver rejects any answers from
signed, secure zones which fail to validate, and returns SERVFAIL to the
client.
Responses may fail to validate for any of several reasons, including
missing, expired, or invalid signatures; a key which does not match the
DS RRset in the parent zone; or an insecure response from a zone which,
according to its parent, should have been secure.
Zones not protected by DNSSEC are called “insecure,” and these zones seamlessly
coexist with signed zones.
When the validator receives a response from an unsigned zone that has
a signed parent, it must confirm with the parent that the zone was
intentionally left unsigned. It does this by verifying, via signed
and validated NSEC/NSEC3 records, that the parent zone contains no
DS records for the child.
If the validator can prove that the zone is insecure, then the
response is accepted. However, if it cannot, the validator must assume an
insecure response to be a forgery; it rejects the response and logs
an error.
The logged error reads “insecurity proof failed” and “got insecure
response; parent indicates it should be secure.”
DNS NOTIFY is a mechanism that allows primary servers to notify their
secondary servers of changes to a zone’s data. In response to a NOTIFY
from a primary server, the secondary checks to see that its version of
the zone is the current version and, if not, initiates a zone transfer.
For more information about DNS NOTIFY, see the description of the
notify option in Boolean Options and the
description of the zone option also-notify in Zone Transfers.
The NOTIFY protocol is specified in RFC 1996.
Note
As a secondary zone can also be a primary to other secondaries, named, by
default, sends NOTIFY messages for every zone it loads.
Specifying notifyprimary-only; causes named to only send
NOTIFY for primary zones that it loads.
Dynamic update is a method for adding, replacing, or deleting records in
a primary server by sending it a special form of DNS messages. The format
and meaning of these messages is specified in RFC 2136.
Dynamic update is enabled by including an allow-update or an
update-policy clause in the zone statement.
If the zone’s update-policy is set to local, updates to the zone
are permitted for the key local-ddns, which is generated by
named at startup. See Dynamic Update Policies for more details.
Dynamic updates using Kerberos-signed requests can be made using the
TKEY/GSS protocol, either by setting the tkey-gssapi-keytab option
or by setting both the tkey-gssapi-credential and
tkey-domain options. Once enabled, Kerberos-signed requests are
matched against the update policies for the zone, using the Kerberos
principal as the signer for the request.
Updating of secure zones (zones using DNSSEC) follows RFC 3007: RRSIG,
NSEC, and NSEC3 records affected by updates are automatically regenerated
by the server using an online zone key. Update authorization is based on
transaction signatures and an explicit server policy.
All changes made to a zone using dynamic update are stored in the zone’s
journal file. This file is automatically created by the server when the
first dynamic update takes place. The name of the journal file is formed
by appending the extension .jnl to the name of the corresponding
zone file unless specifically overridden. The journal file is in a
binary format and should not be edited manually.
The server also occasionally writes (“dumps”) the complete contents
of the updated zone to its zone file. This is not done immediately after
each dynamic update because that would be too slow when a large zone is
updated frequently. Instead, the dump is delayed by up to 15 minutes,
allowing additional updates to take place. During the dump process,
transient files are created with the extensions .jnw and
.jbk; under ordinary circumstances, these are removed when the
dump is complete, and can be safely ignored.
When a server is restarted after a shutdown or crash, it replays the
journal file to incorporate into the zone any updates that took place
after the last zone dump.
Changes that result from incoming incremental zone transfers are also
journaled in a similar way.
The zone files of dynamic zones cannot normally be edited by hand
because they are not guaranteed to contain the most recent dynamic
changes; those are only in the journal file. The only way to ensure
that the zone file of a dynamic zone is up-to-date is to run
rndcstop.
To make changes to a dynamic zone manually, follow these steps:
first, disable dynamic updates to the zone using
rndcfreezezone. This updates the zone file with the
changes stored in its .jnl file. Then, edit the zone file. Finally, run
rndcthawzone to reload the changed zone and re-enable dynamic
updates.
rndcsynczone updates the zone file with changes from the
journal file without stopping dynamic updates; this may be useful for
viewing the current zone state. To remove the .jnl file after
updating the zone file, use rndcsync-clean.
The incremental zone transfer (IXFR) protocol is a way for secondary servers
to transfer only changed data, instead of having to transfer an entire
zone. The IXFR protocol is specified in RFC 1995.
When acting as a primary server, BIND 9 supports IXFR for those zones where the
necessary change history information is available. These include primary
zones maintained by dynamic update and secondary zones whose data was
obtained by IXFR. For manually maintained primary zones, and for secondary
zones obtained by performing a full zone transfer (AXFR), IXFR is
supported only if the option ixfr-from-differences is set to
yes.
When acting as a secondary server, BIND 9 attempts to use IXFR unless it is
explicitly disabled. For more information about disabling IXFR, see the
description of the request-ixfr clause of the server statement.
When a secondary server receives a zone via AXFR, it creates a new copy of the
zone database and then swaps it into place; during the loading process, queries
continue to be served from the old database with no interference. When receiving
a zone via IXFR, however, changes are applied to the running zone, which may
degrade query performance during the transfer. If a server receiving an IXFR
request determines that the response size would be similar in size to an AXFR
response, it may wish to send AXFR instead. The threshold at which this
determination is made can be configured using the
max-ixfr-ratio option.
Setting up different views of the DNS space to internal
and external resolvers is usually referred to as a split DNS setup.
There are several reasons an organization might want to set up its DNS
this way.
One common reason to use split DNS is to hide
“internal” DNS information from “external” clients on the Internet.
There is some debate as to whether this is actually useful.
Internal DNS information leaks out in many ways (via email headers, for
example) and most savvy “attackers” can find the information they need
using other means. However, since listing addresses of internal servers
that external clients cannot possibly reach can result in connection
delays and other annoyances, an organization may choose to use split
DNS to present a consistent view of itself to the outside world.
Another common reason for setting up a split DNS system is to allow
internal networks that are behind filters or in RFC 1918 space (reserved
IP space, as documented in RFC 1918) to resolve DNS on the Internet.
Split DNS can also be used to allow mail from outside back into the
internal network.
Let’s say a company named Example, Inc. (example.com) has several
corporate sites that have an internal network with reserved Internet
Protocol (IP) space and an external demilitarized zone (DMZ), or
“outside” section of a network, that is available to the public.
Example, Inc. wants its internal clients to be able to resolve
external hostnames and to exchange mail with people on the outside. The
company also wants its internal resolvers to have access to certain
internal-only zones that are not available at all outside of the
internal network.
To accomplish this, the company sets up two sets of name
servers. One set is on the inside network (in the reserved IP
space) and the other set is on bastion hosts, which are “proxy”
hosts in the DMZ that can talk to both sides of its network.
The internal servers are configured to forward all queries, except
queries for site1.internal, site2.internal,
site1.example.com, and site2.example.com, to the servers in the
DMZ. These internal servers have complete sets of information for
site1.example.com, site2.example.com, site1.internal, and
site2.internal.
To protect the site1.internal and site2.internal domains, the
internal name servers must be configured to disallow all queries to
these domains from any external hosts, including the bastion hosts.
The external servers, which are on the bastion hosts, are configured
to serve the “public” version of the site1.example.com and site2.example.com
zones. This could include things such as the host records for public
servers (www.example.com and ftp.example.com) and mail exchange
(MX) records (a.mx.example.com and b.mx.example.com).
In addition, the public site1.example.com and site2.example.com zones should
have special MX records that contain wildcard (*) records pointing to
the bastion hosts. This is needed because external mail servers
have no other way of determining how to deliver mail to those internal
hosts. With the wildcard records, the mail is delivered to the
bastion host, which can then forward it on to internal hosts.
Here’s an example of a wildcard MX record:
*INMX10external1.example.com.
Now that they accept mail on behalf of anything in the internal network,
the bastion hosts need to know how to deliver mail to internal
hosts. The resolvers on the bastion
hosts need to be configured to point to the internal name servers
for DNS resolution.
Queries for internal hostnames are answered by the internal servers,
and queries for external hostnames are forwarded back out to the DNS
servers on the bastion hosts.
For all of this to work properly, internal clients need to be
configured to query only the internal name servers for DNS queries.
This could also be enforced via selective filtering on the network.
If everything has been set properly, Example, Inc.’s internal clients
are now able to:
Look up any hostnames in the site1.example.com and site2.example.com
zones.
Look up any hostnames in the site1.internal and
site2.internal domains.
Look up any hostnames on the Internet.
Exchange mail with both internal and external users.
Hosts on the Internet are able to:
Look up any hostnames in the site1.example.com and site2.example.com
zones.
Exchange mail with anyone in the site1.example.com and site2.example.com
zones.
Here is an example configuration for the setup just described above.
Note that this is only configuration information; for information on how
to configure the zone files, see Sample Configurations.
TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS
messages, originally specified in RFC 2845. It allows DNS messages to be
cryptographically signed using a shared secret. TSIG can be used in any
DNS transaction, as a way to restrict access to certain server functions
(e.g., recursive queries) to authorized clients when IP-based access
control is insufficient or needs to be overridden, or as a way to ensure
message authenticity when it is critical to the integrity of the server,
such as with dynamic UPDATE messages or zone transfers from a primary to
a secondary server.
This section is a guide to setting up TSIG in BIND. It describes the
configuration syntax and the process of creating TSIG keys.
named supports TSIG for server-to-server communication, and some of
the tools included with BIND support it for sending messages to
named:
TSIG keys can be generated using the tsig-keygen command; the output
of the command is a key directive suitable for inclusion in
named.conf. The key name, algorithm, and size can be specified by
command-line parameters; the defaults are “tsig-key”, HMAC-SHA256, and
256 bits, respectively.
Any string which is a valid DNS name can be used as a key name. For
example, a key to be shared between servers called host1 and host2
could be called “host1-host2.”, and this key can be generated using:
$ tsig-keygen host1-host2. > host1-host2.key
This key may then be copied to both hosts. The key name and secret must
be identical on both hosts. (Note: copying a shared secret from one
server to another is beyond the scope of the DNS. A secure transport
mechanism should be used: secure FTP, SSL, ssh, telephone, encrypted
email, etc.)
tsig-keygen can also be run as ddns-confgen, in which case its
output includes additional configuration text for setting up dynamic DNS
in named. See ddns-confgen - TSIG key generation tool for details.
(This is the same key generated above using tsig-keygen.)
Since this text contains a secret, it is recommended that either
named.conf not be world-readable, or that the key directive be
stored in a file which is not world-readable and which is included in
named.conf via the include directive.
Once a key has been added to named.conf and the server has been
restarted or reconfigured, the server can recognize the key. If the
server receives a message signed by the key, it is able to verify
the signature. If the signature is valid, the response is signed
using the same key.
TSIG keys that are known to a server can be listed using the command
rndctsig-list.
A server sending a request to another server must be told whether to use
a key, and if so, which key to use.
For example, a key may be specified for each server in the primaries
statement in the definition of a secondary zone; in this case, all SOA QUERY
messages, NOTIFY messages, and zone transfer requests (AXFR or IXFR)
are signed using the specified key. Keys may also be specified in
the also-notify statement of a primary or secondary zone, causing NOTIFY
messages to be signed using the specified key.
Keys can also be specified in a server directive. Adding the
following on host1, if the IP address of host2 is 10.1.2.3, would
cause all requests from host1 to host2, including normal DNS
queries, to be signed using the host1-host2. key:
server10.1.2.3{keys{host1-host2.;};};
Multiple keys may be present in the keys statement, but only the
first one is used. As this directive does not contain secrets, it can be
used in a world-readable file.
Requests sent by host2 to host1 would not be signed, unless a
similar server directive were in host2’s configuration file.
When any server sends a TSIG-signed DNS request, it expects the
response to be signed with the same key. If a response is not signed, or
if the signature is not valid, the response is rejected.
TSIG keys may be specified in ACL definitions and ACL directives such as
allow-query, allow-transfer, and allow-update. The above key
would be denoted in an ACL element as keyhost1-host2.
Here is an example of an allow-update directive using a TSIG key:
Processing of TSIG-signed messages can result in several errors:
If a TSIG-aware server receives a message signed by an unknown key,
the response will be unsigned, with the TSIG extended error code set
to BADKEY.
If a TSIG-aware server receives a message from a known key but with
an invalid signature, the response will be unsigned, with the TSIG
extended error code set to BADSIG.
If a TSIG-aware server receives a message with a time outside of the
allowed range, the response will be signed but the TSIG extended
error code set to BADTIME, and the time values will be adjusted so
that the response can be successfully verified.
In all of the above cases, the server returns a response code of
NOTAUTH (not authenticated).
TKEY (Transaction KEY) is a mechanism for automatically negotiating a
shared secret between two hosts, originally specified in RFC 2930.
There are several TKEY “modes” that specify how a key is to be generated
or assigned. BIND 9 implements only one of these modes: Diffie-Hellman
key exchange. Both hosts are required to have a KEY record with
algorithm DH (though this record is not required to be present in a
zone).
The TKEY process is initiated by a client or server by sending a query
of type TKEY to a TKEY-aware server. The query must include an
appropriate KEY record in the additional section, and must be signed
using either TSIG or SIG(0) with a previously established key. The
server’s response, if successful, contains a TKEY record in its
answer section. After this transaction, both participants have
enough information to calculate a shared secret using Diffie-Hellman key
exchange. The shared secret can then be used to sign subsequent
transactions between the two servers.
TSIG keys known by the server, including TKEY-negotiated keys, can be
listed using rndctsig-list.
TKEY-negotiated keys can be deleted from a server using
rndctsig-delete. This can also be done via the TKEY protocol
itself, by sending an authenticated TKEY query specifying the “key
deletion” mode.
BIND partially supports DNSSEC SIG(0) transaction signatures as
specified in RFC 2535 and RFC 2931. SIG(0) uses public/private keys to
authenticate messages. Access control is performed in the same manner as with
TSIG keys; privileges can be granted or denied in ACL directives based
on the key name.
When a SIG(0) signed message is received, it is only verified if
the key is known and trusted by the server. The server does not attempt
to recursively fetch or validate the key.
SIG(0) signing of multiple-message TCP streams is not supported.
The only tool shipped with BIND 9 that generates SIG(0) signed messages
is nsupdate.
BIND is able to maintain DNSSEC trust anchors using RFC 5011 key
management. This feature allows named to keep track of changes to
critical DNSSEC keys without any need for the operator to make changes
to configuration files.
To configure a validating resolver to use RFC 5011 to maintain a trust
anchor, configure the trust anchor using a trust-anchors statement and
the initial-key keyword. Information about this can be found in
trust-anchors Statement Definition and Usage.
To set up an authoritative zone for RFC 5011 trust anchor maintenance,
generate two (or more) key signing keys (KSKs) for the zone. Sign the
zone with one of them; this is the “active” KSK. All KSKs which do not
sign the zone are “stand-by” keys.
Any validating resolver which is configured to use the active KSK as an
RFC 5011-managed trust anchor takes note of the stand-by KSKs in the
zone’s DNSKEY RRset, and stores them for future reference. The resolver
rechecks the zone periodically; after 30 days, if the new key is
still there, the key is accepted by the resolver as a valid
trust anchor for the zone. Anytime after this 30-day acceptance timer
has completed, the active KSK can be revoked, and the zone can be
“rolled over” to the newly accepted key.
The easiest way to place a stand-by key in a zone is to use the “smart
signing” features of dnssec-keygen and dnssec-signzone. If a key
exists with a publication date in the past, but an activation date which is
unset or in the future, dnssec-signzone-S includes the
DNSKEY record in the zone but does not sign with it:
$ dnssec-keygen -K keys -f KSK -P now -A now+2y example.net
$ dnssec-signzone -S -K keys example.net
To revoke a key, use the command dnssec-revoke. This
adds the REVOKED bit to the key flags and regenerates the K*.key
and K*.private files.
After revoking the active key, the zone must be signed with both the
revoked KSK and the new active KSK. Smart signing takes care of this
automatically.
Once a key has been revoked and used to sign the DNSKEY RRset in which
it appears, that key is never again accepted as a valid trust
anchor by the resolver. However, validation can proceed using the new
active key, which was accepted by the resolver when it was a
stand-by key.
See RFC 5011 for more details on key rollover scenarios.
When a key has been revoked, its key ID changes, increasing by 128 and
wrapping around at 65535. So, for example, the key
“Kexample.com.+005+10000” becomes “Kexample.com.+005+10128”.
If two keys have IDs exactly 128 apart and one is revoked, the two
key IDs will collide, causing several problems. To prevent this,
dnssec-keygen does not generate a new key if another key
which may collide is present. This checking only occurs if the new keys are
written to the same directory that holds all other keys in use for that
zone.
Older versions of BIND 9 did not have this protection. Exercise caution
if using key revocation on keys that were generated by previous
releases, or if using keys stored in multiple directories or on multiple
machines.
It is expected that a future release of BIND 9 will address this problem
in a different way, by storing revoked keys with their original
unrevoked key IDs.
Public Key Cryptography Standard #11 (PKCS#11) defines a
platform-independent API for the control of hardware security modules
(HSMs) and other cryptographic support devices.
BIND 9 is known to work with three HSMs: the AEP Keyper, which has been
tested with Debian Linux, Solaris x86, and Windows Server 2003; the
Thales nShield, tested with Debian Linux; and the Sun SCA 6000
cryptographic acceleration board, tested with Solaris x86. In addition,
BIND can be used with all current versions of SoftHSM, a software-based
HSM simulator library produced by the OpenDNSSEC project.
PKCS#11 uses a “provider library”: a dynamically loadable
library which provides a low-level PKCS#11 interface to drive the HSM
hardware. The PKCS#11 provider library comes from the HSM vendor, and it
is specific to the HSM to be controlled.
There are two available mechanisms for PKCS#11 support in BIND 9:
OpenSSL-based PKCS#11 and native PKCS#11. With OpenSSL-based PKCS#11,
BIND uses a modified version of OpenSSL, which loads the
provider library and operates the HSM indirectly; any cryptographic
operations not supported by the HSM can be carried out by OpenSSL
instead. Native PKCS#11 enables BIND to bypass OpenSSL completely;
BIND loads the provider library itself, and uses the PKCS#11 API to
drive the HSM directly.
Native PKCS#11 mode only works with an HSM capable of carrying out
every cryptographic operation BIND 9 may need. The HSM’s provider
library must have a complete implementation of the PKCS#11 API, so that
all these functions are accessible. As of this writing, only the Thales
nShield HSM and SoftHSMv2 can be used in this fashion. For other HSMs,
including the AEP Keyper, Sun SCA 6000, and older versions of SoftHSM,
use OpenSSL-based PKCS#11. (Note: Eventually, when more HSMs become
capable of supporting native PKCS#11, it is expected that OpenSSL-based
PKCS#11 will be deprecated.)
To build BIND with native PKCS#11, configure it as follows:
$ cd bind9
$ ./configure --enable-native-pkcs11 \
--with-pkcs11=provider-library-path
This causes all BIND tools, including named and the dnssec-*
and pkcs11-* tools, to use the PKCS#11 provider library specified in
provider-library-path for cryptography. (The provider library path can
be overridden using the -E argument in named and the dnssec-* tools,
or the -m argument in the pkcs11-* tools.)
SoftHSMv2, the latest development version of SoftHSM, is available from
https://github.com/opendnssec/SoftHSMv2. It is a software library
developed by the OpenDNSSEC project (https://www.opendnssec.org) which
provides a PKCS#11 interface to a virtual HSM, implemented in the form
of an SQLite3 database on the local filesystem. It provides less security
than a true HSM, but it allows users to experiment with native PKCS#11
when an HSM is not available. SoftHSMv2 can be configured to use either
OpenSSL or the Botan library to perform cryptographic functions, but
when using it for native PKCS#11 in BIND, OpenSSL is required.
By default, the SoftHSMv2 configuration file is prefix/etc/softhsm2.conf
(where prefix is configured at compile time). This location can be
overridden by the SOFTHSM2_CONF environment variable. The SoftHSMv2
cryptographic store must be installed and initialized before using it
with BIND.
$ cd SoftHSMv2
$ configure --with-crypto-backend=openssl --prefix=/opt/pkcs11/usr
$ make
$ make install
$ /opt/pkcs11/usr/bin/softhsm-util --init-token 0 --slot 0 --label softhsmv2
BIND 9 includes a minimal set of tools to operate the HSM, including
pkcs11-keygen to generate a new key pair within the HSM,
pkcs11-list to list objects currently available, pkcs11-destroy
to remove objects, and pkcs11-tokens to list available tokens.
In UNIX/Linux builds, these tools are built only if BIND 9 is configured
with the --with-pkcs11 option. (Note: If --with-pkcs11 is set to yes,
rather than to the path of the PKCS#11 provider, the tools are
built but the provider is left undefined. Use the -m option or the
PKCS11_PROVIDER environment variable to specify the path to the
provider.)
This causes named and other binaries to load the OpenSSL library
from /opt/pkcs11/usr/lib, rather than from the default location. This
step is not necessary when using native PKCS#11.
Some HSMs require other environment variables to be set. For example,
when operating an AEP Keyper, the location of
the “machine” file, which stores information about the Keyper for use by
the provider library, must be specified. If the machine file is in
/opt/Keyper/PKCS11Provider/machine, use:
Such environment variables must be set when running any tool that
uses the HSM, including pkcs11-keygen, pkcs11-list,
pkcs11-destroy, dnssec-keyfromlabel, dnssec-signzone,
dnssec-keygen, and named.
HSM keys can now be created and used. In this case, we will create
a 2048-bit key and give it the label “sample-ksk”:
$ pkcs11-keygen -b 2048 -l sample-ksk
To confirm that the key exists:
$ pkcs11-list
Enter PIN:
object[0]: handle 2147483658 class 3 label[8] 'sample-ksk' id[0]
object[1]: handle 2147483657 class 2 label[8] 'sample-ksk' id[0]
Before using this key to sign a zone, we must create a pair of BIND 9
key files. The dnssec-keyfromlabel utility does this. In this case, we
are using the HSM key “sample-ksk” as the key-signing key for
“example.net”:
The resulting K*.key and K*.private files can now be used to sign the
zone. Unlike normal K* files, which contain both public and private key
data, these files contain only the public key data, plus an
identifier for the private key which remains stored within the HSM.
Signing with the private key takes place inside the HSM.
To generate a second key in the HSM for use as a
zone-signing key, follow the same procedure above, using a different
keylabel, a smaller key size, and omitting -fKSK from the
dnssec-keyfromlabel arguments:
Alternatively, a conventional on-disk key can be generated
using dnssec-keygen:
$ dnssec-keygen example.net
This provides less security than an HSM key, but since HSMs can be slow
or cumbersome to use for security reasons, it may be more efficient to
reserve HSM keys for use in the less frequent key-signing operation. The
zone-signing key can be rolled more frequently, if desired, to
compensate for a reduction in key security. (Note: When using native
PKCS#11, there is no speed advantage to using on-disk keys, as
cryptographic operations are done by the HSM.)
Now the zone can be signed. Please note that, if the -S option is not used for
dnssec-signzone, the contents of both
K*.key files must be added to the zone master file before signing it.
$ dnssec-signzone -S example.net
Enter PIN:
Verifying the zone using the following algorithms:
NSEC3RSASHA1.
Zone signing complete:
Algorithm: NSEC3RSASHA1: ZSKs: 1, KSKs: 1 active, 0 revoked, 0 stand-by
example.net.signed
When using OpenSSL-based PKCS#11, the “engine” to be used by OpenSSL can
be specified in named and all of the BIND dnssec-* tools by
using the -E<engine> command line option. If BIND 9 is built with the
--with-pkcs11 option, this option defaults to “pkcs11”. Specifying the
engine is generally not necessary unless
a different OpenSSL engine is used.
To disable use of the “pkcs11” engine - for
troubleshooting purposes, or because the HSM is unavailable - set
the engine to the empty string. For example:
$ dnssec-signzone -E '' -S example.net
This causes dnssec-signzone to run as if it were compiled without
the --with-pkcs11 option.
When built with native PKCS#11 mode, the “engine” option has a different
meaning: it specifies the path to the PKCS#11 provider library. This may
be useful when testing a new provider library.
For named to dynamically re-sign zones using HSM keys,
and/or to sign new records inserted via nsupdate, named must
have access to the HSM PIN. In OpenSSL-based PKCS#11, this is
accomplished by placing the PIN into the openssl.cnf file (in the above
examples, /opt/pkcs11/usr/ssl/openssl.cnf).
The location of the openssl.cnf file can be overridden by setting the
OPENSSL_CONF environment variable before running named.
This also allows the dnssec-\* tools to access the HSM without PIN
entry. (The pkcs11-\* tools access the HSM directly, not via OpenSSL, so
a PIN is still required to use them.)
In native PKCS#11 mode, the PIN can be provided in a file specified as
an attribute of the key’s label. For example, if a key had the label
pkcs11:object=local-zsk;pin-source=/etc/hsmpin, then the PIN would
be read from the file /etc/hsmpin.
Warning
Placing the HSM’s PIN in a text file in this manner may reduce the
security advantage of using an HSM. Use caution
when configuring the system in this way.
Dynamically Loadable Zones (DLZ) are an extension to BIND 9 that allows
zone data to be retrieved directly from an external database. There is
no required format or schema. DLZ drivers exist for several different
database backends, including PostgreSQL, MySQL, and LDAP, and can be
written for any other.
Historically, DLZ drivers had to be statically linked with the named
binary and were turned on via a configure option at compile time (for
example, configure--with-dlz-ldap). The drivers
provided in the BIND 9 tarball in contrib/dlz/drivers are still
linked this way.
In BIND 9.8 and higher, it is possible to link some DLZ modules
dynamically at runtime, via the DLZ “dlopen” driver, which acts as a
generic wrapper around a shared object implementing the DLZ API. The
“dlopen” driver is linked into named by default, so configure
options are no longer necessary when using these dynamically linkable
drivers; they are still needed for the older drivers in
contrib/dlz/drivers.
The DLZ module provides data to named in text
format, which is then converted to DNS wire format by named. This
conversion, and the lack of any internal caching, places significant
limits on the query performance of DLZ modules. Consequently, DLZ is not
recommended for use on high-volume servers. However, it can be used in a
hidden primary configuration, with secondaries retrieving zone updates via
AXFR. Note, however, that DLZ has no built-in support for DNS notify;
secondary servers are not automatically informed of changes to the zones in the
database.
This specifies a DLZ module to search when answering queries; the module
is implemented in driver.so and is loaded at runtime by the dlopen
DLZ driver. Multiple dlz statements can be specified; when answering
a query, all DLZ modules with search set to yes are queried
to see whether they contain an answer for the query name. The best
available answer is returned to the client.
The search option in the above example can be omitted, because
yes is the default value.
If search is set to no, this DLZ module is not searched
for the best match when a query is received. Instead, zones in this DLZ
must be separately specified in a zone statement. This allows users to
configure a zone normally using standard zone-option semantics, but
specify a different database backend for storage of the zone’s data.
For example, to implement NXDOMAIN redirection using a DLZ module for
backend storage of redirection rules:
For guidance in the implementation of DLZ modules, the directory
contrib/dlz/example contains a basic dynamically linkable DLZ
module - i.e., one which can be loaded at runtime by the “dlopen” DLZ
driver. The example sets up a single zone, whose name is passed to the
module as an argument in the dlz statement:
In the above example, the module is configured to create a zone
“example.nil”, which can answer queries and AXFR requests and accept
DDNS updates. At runtime, prior to any updates, the zone contains an
SOA, NS, and a single A record at the apex:
The sample driver can retrieve information about the
querying client and alter its response on the basis of this
information. To demonstrate this feature, the example driver responds to
queries for “source-addr.``zonename``>/TXT” with the source address of
the query. Note, however, that this record will not be included in
AXFR or ANY responses. Normally, this feature is used to alter
responses in some other fashion, e.g., by providing different address
records for a particular name depending on the network from which the
query arrived.
Documentation of the DLZ module API can be found in
contrib/dlz/example/README. This directory also contains the header
file dlz_minimal.h, which defines the API and should be included by
any dynamically linkable DLZ module.
Dynamic Database, or DynDB, is an extension to BIND 9 which, like DLZ (see
Dynamically Loadable Zones (DLZ)), allows zone data to be retrieved from an external
database. Unlike DLZ, a DynDB module provides a full-featured BIND zone
database interface. Where DLZ translates DNS queries into real-time
database lookups, resulting in relatively poor query performance, and is
unable to handle DNSSEC-signed data due to its limited API, a DynDB
module can pre-load an in-memory database from the external data source,
providing the same performance and functionality as zones served
natively by BIND.
A DynDB database is configured with a dyndb statement in
named.conf:
dyndbexample"driver.so"{parameters};
The file driver.so is a DynDB module which implements the full DNS
database API. Multiple dyndb statements can be specified, to load
different drivers or multiple instances of the same driver. Zones
provided by a DynDB module are added to the view’s zone table, and are
treated as normal authoritative zones when BIND responds to
queries. Zone configuration is handled internally by the DynDB module.
The parameters are passed as an opaque string to the DynDB module’s
initialization routine. Configuration syntax differs depending on
the driver.
For guidance in the implementation of DynDB modules, the directory
bin/tests/system/dyndb/driver contains a basic DynDB module. The
example sets up two zones, whose names are passed to the module as
arguments in the dyndb statement:
dyndbsample"sample.so"{example.nil.arpa.};
In the above example, the module is configured to create a zone,
“example.nil”, which can answer queries and AXFR requests and accept
DDNS updates. At runtime, prior to any updates, the zone contains an
SOA, NS, and a single A record at the apex:
When the zone is updated dynamically, the DynDB module determines
whether the updated RR is an address (i.e., type A or AAAA); if so,
it automatically updates the corresponding PTR record in a reverse
zone. Note that updates are not stored permanently; all updates are lost when the
server is restarted.
A “catalog zone” is a special DNS zone that contains a list of other
zones to be served, along with their configuration parameters. Zones
listed in a catalog zone are called “member zones.” When a catalog zone
is loaded or transferred to a secondary server which supports this
functionality, the secondary server creates the member zones
automatically. When the catalog zone is updated (for example, to add or
delete member zones, or change their configuration parameters), those
changes are immediately put into effect. Because the catalog zone is a
normal DNS zone, these configuration changes can be propagated using the
standard AXFR/IXFR zone transfer mechanism.
Normally, if a zone is to be served by a secondary server, the
named.conf file on the server must list the zone, or the zone must
be added using rndcaddzone. In environments with a large number of
secondary servers, and/or where the zones being served are changing
frequently, the overhead involved in maintaining consistent zone
configuration on all the secondary servers can be significant.
A catalog zone is a way to ease this administrative burden: it is a DNS
zone that lists member zones that should be served by secondary servers.
When a secondary server receives an update to the catalog zone, it adds,
removes, or reconfigures member zones based on the data received.
To use a catalog zone, it must first be set up as a normal zone on both the
primary and secondary servers that are configured to use it. It
must also be added to a catalog-zones list in the options or
view statement in named.conf. This is comparable to the way a
policy zone is configured as a normal zone and also listed in a
response-policy statement.
To use the catalog zone feature to serve a new member zone:
Set up the member zone to be served on the primary as normal. This
can be done by editing named.conf or by running
rndcaddzone.
Add an entry to the catalog zone for the new member zone. This can
be done by editing the catalog zone’s zone file and running
rndcreload, or by updating the zone using nsupdate.
The change to the catalog zone is propagated from the primary to all
secondaries using the normal AXFR/IXFR mechanism. When the secondary receives the
update to the catalog zone, it detects the entry for the new member
zone, creates an instance of that zone on the secondary server, and points
that instance to the masters specified in the catalog zone data. The
newly created member zone is a normal secondary zone, so BIND
immediately initiates a transfer of zone contents from the primary. Once
complete, the secondary starts serving the member zone.
Removing a member zone from a secondary server requires only
deleting the member zone’s entry in the catalog zone; the change to the
catalog zone is propagated to the secondary server using the normal
AXFR/IXFR transfer mechanism. The secondary server, on processing the
update, notices that the member zone has been removed, stops
serving the zone, and removes it from its list of configured zones.
However, removing the member zone from the primary server must be done
by editing the configuration file or running
rndcdelzone.
This statement specifies that the zone catalog.example is a catalog
zone. This zone must be properly configured in the same view. In most
configurations, it would be a secondary zone.
The options following the zone name are not required, and may be
specified in any order.
default-masters
This option defines the default primaries for member
zones listed in a catalog zone, and can be overridden by options within
a catalog zone. If no such options are included, then member zones
transfer their contents from the servers listed in this option.
in-memory
This option, if set to yes, causes member zones to be
stored only in memory. This is functionally equivalent to configuring a
secondary zone without a file option. The default is no; member
zones’ content is stored locally in a file whose name is
automatically generated from the view name, catalog zone name, and
member zone name.
zone-directory
This option causes local copies of member zones’ zone files to be
stored in the specified directory, if in-memory is not set to
yes. The default is to store zone files in the server’s working
directory. A non-absolute pathname in zone-directory is assumed
to be relative to the working directory.
min-update-interval
This option sets the minimum interval between updates to catalog
zones, in seconds. If an update to a catalog zone (for example, via
IXFR) happens less than min-update-interval seconds after the
most recent update, the changes are not carried out until this
interval has elapsed. The default is 5 seconds.
Catalog zones are defined on a per-view basis. Configuring a non-empty
catalog-zones statement in a view automatically turns on
allow-new-zones for that view. This means that rndcaddzone
and rndcdelzone also work in any view that supports catalog
zones.
A catalog zone is a regular DNS zone; therefore, it must have a single
SOA and at least one NS record.
A record stating the version of the catalog zone format is also
required. If the version number listed is not supported by the server,
then a catalog zone may not be used by that server.
Note that this record must have the domain name
version.catalog-zone-name. The data
stored in a catalog zone is indicated by the domain name label
immediately before the catalog zone domain.
Catalog zone options can be set either globally for the whole catalog
zone or for a single member zone. Global options override the settings
in the configuration file, and member zone options override global
options.
Global options are set at the apex of the catalog zone, e.g.:
masters.catalog.example.INAAAA2001:db8::1
BIND currently supports the following options:
A simple masters definition:
masters.catalog.example.INA192.0.2.1
This option defines a primary server for the member zones, which can be
either an A or AAAA record. If multiple primaries are set, the order in
which they are used is random.
This option defines a primary server for the member zone with a TSIG
key set. The TSIG key must be configured in the configuration file.
label can be any valid DNS label.
allow-query and allow-transfer ACLs:
allow-query.catalog.example. IN APL 1:10.0.0.1/24
allow-transfer.catalog.example. IN APL !1:10.0.0.1/32 1:10.0.0.0/24
These options are the equivalents of allow-query and
allow-transfer in a zone declaration in the named.conf
configuration file. The ACL is processed in order; if there is no
match to any rule, the default policy is to deny access. For the
syntax of the APL RR, see RFC 3123.
A member zone is added by including a PTR resource record in the
zones sub-domain of the catalog zone. The record label is a
SHA-1 hash of the member zone name in wire format. The target of the
PTR record is the member zone name. For example, to add the member zone
domain.example:
The hash is necessary to identify options for a specific member zone.
The member zone-specific options are defined the same way as global
options, but in the member zone subdomain:
Options defined for a specific zone override the
global options defined in the catalog zone. These in turn override the
global options defined in the catalog-zones statement in the
configuration file.
Note that none of the global records for an option are inherited if any
records are defined for that option for the specific zone. For example,
if the zone had a masters record of type A but not AAAA, it
would not inherit the type AAAA record from the global option.
BIND 9 fully supports all currently defined forms of IPv6 name-to-address
and address-to-name lookups. It also uses IPv6 addresses to
make queries when running on an IPv6-capable system.
For forward lookups, BIND 9 supports only AAAA records. RFC 3363
deprecated the use of A6 records, and client-side support for A6 records
was accordingly removed from BIND 9. However, authoritative BIND 9 name
servers still load zone files containing A6 records correctly, answer
queries for A6 records, and accept zone transfer for a zone containing
A6 records.
For IPv6 reverse lookups, BIND 9 supports the traditional “nibble”
format used in the ip6.arpa domain, as well as the older, deprecated
ip6.int domain. Older versions of BIND 9 supported the “binary label”
(also known as “bitstring”) format, but support of binary labels has
been completely removed per RFC 3363. Many applications in BIND 9 do not
understand the binary label format at all anymore, and return an
error if one is given. In particular, an authoritative BIND 9 name server will
not load a zone file containing binary labels.
The IPv6 AAAA record is a parallel to the IPv4 A record, and, unlike the
deprecated A6 record, specifies the entire IPv6 address in a single
record. For example:
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
Use of IPv4-in-IPv6 mapped addresses is not recommended. If a host has
an IPv4 address, use an A record, not a AAAA, with
::ffff:192.168.42.1 as the address.
When looking up an address in nibble format, the address components are
simply reversed, just as in IPv4, and ip6.arpa. is appended to the
resulting name. For example, the following commands produce a reverse name
lookup for a host with address 2001:db8::1:
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
host.example.com. )
Access Control Lists (ACLs) are address match lists that can be set up
and nicknamed for future use in allow-notify, allow-query,
allow-query-on, allow-recursion, blackhole,
allow-transfer, match-clients, etc.
ACLs give users finer control over who can access the
name server, without cluttering up configuration files with huge lists of
IP addresses.
It is a good idea to use ACLs, and to control access.
Limiting access to the server by outside parties can help prevent
spoofing and denial of service (DoS) attacks against the server.
ACLs match clients on the basis of up to three characteristics: 1) The
client’s IP address; 2) the TSIG or SIG(0) key that was used to sign the
request, if any; and 3) an address prefix encoded in an EDNS
Client-Subnet option, if any.
Here is an example of ACLs based on client addresses:
This allows authoritative queries for example.com from any address,
but recursive queries only from the networks specified in our-nets,
and no queries at all from the networks specified in bogusnets.
In addition to network addresses and prefixes, which are matched against
the source address of the DNS request, ACLs may include key
elements, which specify the name of a TSIG or SIG(0) key.
When BIND 9 is built with GeoIP support, ACLs can also be used for
geographic access restrictions. This is done by specifying an ACL
element of the form: geoipdbdatabasefieldvalue.
The field parameter indicates which field to search for a match. Available fields
are country, region, city, continent, postal (postal code),
metro (metro code), area (area code), tz (timezone), isp,
asnum, and domain.
value is the value to search for within the database. A string may be quoted
if it contains spaces or other special characters. An asnum search for
autonomous system number can be specified using the string “ASNNNN” or the
integer NNNN. If a country search is specified with a string that is two characters
long, it must be a standard ISO-3166-1 two-letter country code; otherwise,
it is interpreted as the full name of the country. Similarly, if
region is the search term and the string is two characters long, it is treated as a
standard two-letter state or province abbreviation; otherwise, it is treated as the
full name of the state or province.
The database field indicates which GeoIP database to search for a match. In
most cases this is unnecessary, because most search fields can only be found in
a single database. However, searches for continent or country can be
answered from either the city or country databases, so for these search
types, specifying a database forces the query to be answered from that
database and no other. If a database is not specified, these queries
are first answered from the city database if it is installed, and then from the country
database if it is installed. Valid database names are country,
city, asnum, isp, and domain.
Some example GeoIP ACLs:
geoipcountryUS;geoipcountryJP;geoipdbcountrycountryCanada;geoipregionWA;geoipcity"San Francisco";geoipregionOklahoma;geoippostal95062;geoiptz"America/Los_Angeles";geoiporg"Internet Systems Consortium";
ACLs use a “first-match” logic rather than “best-match”; if an address
prefix matches an ACL element, then that ACL is considered to have
matched even if a later element would have matched more specifically.
For example, the ACL {10/8;!10.0.0.1;} would actually match a
query from 10.0.0.1, because the first element indicates that the query
should be accepted, and the second element is ignored.
When using “nested” ACLs (that is, ACLs included or referenced within
other ACLs), a negative match of a nested ACL tells the containing ACL to
continue looking for matches. This enables complex ACLs to be
constructed, in which multiple client characteristics can be checked at
the same time. For example, to construct an ACL which allows a query
only when it originates from a particular network and only when it is
signed with a particular key, use:
allow-query { !{ !10/8; any; }; key example; };
Within the nested ACL, any address that is not in the 10/8 network
prefix is rejected, which terminates the processing of the ACL.
Any address that is in the 10/8 network prefix is accepted, but
this causes a negative match of the nested ACL, so the containing ACL
continues processing. The query is accepted if it is signed by
the key example, and rejected otherwise. The ACL, then, only
matches when both conditions are true.
On Unix servers, it is possible to run BIND in a chrooted environment
(using the chroot() function) by specifying the -t option for
named. This can help improve system security by placing BIND in a
“sandbox,” which limits the damage done if a server is compromised.
Another useful feature in the Unix version of BIND is the ability to run
the daemon as an unprivileged user (-u user). We suggest running
as an unprivileged user when using the chroot feature.
Here is an example command line to load BIND in a chroot sandbox,
/var/named, and to run namedsetuid to user 202:
For a chroot environment to work properly in a particular
directory (for example, /var/named), the
environment must include everything BIND needs to run. From BIND’s
point of view, /var/named is the root of the filesystem;
the values of options like directory and pid-file
must be adjusted to account for this.
Unlike with earlier versions of BIND,
named does not typically need to be compiled statically, nor do shared libraries need to be installed under the new
root. However, depending on the operating system, it may be necessary to set
up locations such as /dev/zero, /dev/random, /dev/log, and
/etc/localtime.
Prior to running the named daemon, use the touch utility (to
change file access and modification times) or the chown utility (to
set the user id and/or group id) on files where BIND should
write.
Note
If the named daemon is running as an unprivileged user, it
cannot bind to new restricted ports if the server is
reloaded.
Access to the dynamic update facility should be strictly limited. In
earlier versions of BIND, the only way to do this was based on the IP
address of the host requesting the update, by listing an IP address or
network prefix in the allow-update zone option. This method is
insecure, since the source address of the update UDP packet is easily
forged. Also note that if the IP addresses allowed by the
allow-update option include the address of a secondary server which
performs forwarding of dynamic updates, the primary can be trivially
attacked by sending the update to the secondary, which forwards it to
the primary with its own source IP address - causing the primary to approve
it without question.
For these reasons, we strongly recommend that updates be
cryptographically authenticated by means of transaction signatures
(TSIG). That is, the allow-update option should list only TSIG key
names, not IP addresses or network prefixes. Alternatively, the
update-policy option can be used.
Some sites choose to keep all dynamically updated DNS data in a
subdomain and delegate that subdomain to a separate zone. This way, the
top-level zone containing critical data, such as the IP addresses of
public web and mail servers, need not allow dynamic updates at all.
It’s Not Working; How Can I Figure Out What’s Wrong?
The best solution to installation and configuration issues is to
take preventive measures by setting up logging files beforehand. The
log files provide hints and information that can be used to
identify anything that went wrong and fix the problem.
EDNS (Extended DNS) is a standard that was first specified in 1999. It
is required for DNSSEC validation, DNS COOKIE options, and other
features. There are broken and outdated DNS servers and firewalls still
in use which misbehave when queried with EDNS; for example, they may
drop EDNS queries rather than replying with FORMERR. BIND and other
recursive name servers have traditionally employed workarounds in this
situation, retrying queries in different ways and eventually falling
back to plain DNS queries without EDNS.
Such workarounds cause unnecessary resolution delays, increase code
complexity, and prevent deployment of new DNS features. In February
2019, all major DNS software vendors removed these
workarounds; see https://dnsflagday.net/2019 for further details. This change
was implemented in BIND as of release 9.14.0.
As a result, some domains may be non-resolvable without manual
intervention. In these cases, resolution can be restored by adding
server clauses for the offending servers, or by specifying ednsno or
send-cookieno, depending on the specific noncompliance.
To determine which server clause to use, run the following commands
to send queries to the authoritative servers for the broken domain:
If the first command fails but the second succeeds, the server most
likely needs send-cookieno. If the first two fail but the third
succeeds, then the server needs EDNS to be fully disabled with
ednsno.
Please contact the administrators of noncompliant domains and encourage
them to upgrade their broken DNS servers.
Zone serial numbers are just numbers — they are not date-related. However, many
people set them to a number that represents a date, usually of the
form YYYYMMDDRR. Occasionally they make a mistake and set the serial number to a
date in the future, then try to correct it by setting it to the
current date. This causes problems because serial numbers are used to
indicate that a zone has been updated. If the serial number on the secondary
server is lower than the serial number on the primary, the secondary server
attempts to update its copy of the zone.
Setting the serial number to a lower number on the primary server than the one
on the secondary server means that the secondary will not perform updates to its
copy of the zone.
The solution to this is to add 2147483647 (2^31-1) to the number, reload
the zone and make sure all secondaries have updated to the new zone serial
number, then reset it to the desired number and reload the
zone again.
Internet Systems Consortium (ISC) offers annual support agreements
for BIND 9, ISC DHCP, and Kea DHCP.
All paid support contracts include advance security notifications; some levels include
service level agreements (SLAs), premium software features, and increased priority on bug fixes
and feature requests.
BIND 9.16 (Extended Support Version) is a stable branch of BIND. This
document summarizes significant changes since the last production
release on that branch. Please see the CHANGES file for a more detailed
list of changes and bug fixes.
As of BIND 9.13/9.14, BIND has adopted the “odd-unstable/even-stable”
release numbering convention. BIND 9.16 contains new features that were
added during the BIND 9.15 development process. Henceforth, the 9.16
branch will be limited to bug fixes, and new feature development will
proceed in the unstable 9.17 branch.
The latest versions of BIND 9 software can always be found at
https://www.isc.org/download/. There you will find additional
information about each release, source code, and pre-compiled versions
for Microsoft Windows operating systems.
BIND crashes on startup when linked against libuv 1.36. This issue is
related to recvmmsg() support in libuv, which was first included
in libuv 1.35. The problem was addressed in libuv 1.37, but the
relevant libuv code change requires a special flag to be set during
library initialization in order for recvmmsg() support to be
enabled. This BIND release sets that special flag when required, so
recvmmsg() support is now enabled when BIND is compiled against
either libuv 1.35 or libuv 1.37+; libuv 1.36 is still not usable with
BIND. [GL #1761][GL #1797]
UDP network ports used for listening can no longer simultaneously be
used for sending traffic. An example configuration which triggers this
issue would be one which uses the same address:port pair for
listen-on(-v6) statements as for notify-source(-v6) or
transfer-source(-v6). While this issue affects all operating
systems, it only triggers log messages (e.g. “unable to create
dispatch for reserved port”) on some of them. There are currently no
plans to make such a combination of settings work again.
libuv support for receiving multiple UDP messages in a single
recvmmsg() system call has been tweaked several times between
libuv versions 1.35.0 and 1.40.0; the current recommended libuv
version is 1.40.0 or higher. New rules are now in effect for running
with a different version of libuv than the one used at compilation
time. These rules may trigger a fatal error at startup:
Building against or running with libuv versions 1.35.0 and 1.36.0 is
now a fatal error.
Running with libuv version higher than 1.34.2 is now a fatal error
when named is built against libuv version 1.34.2 or lower.
Running with libuv version higher than 1.39.0 is now a fatal error
when named is built against libuv version 1.37.0, 1.38.0,
1.38.1, or 1.39.0.
This prevents the use of libuv versions that may trigger an assertion
failure when receiving multiple UDP messages in a single system call.
[GL #3840]
named could crash with an assertion failure when adding a
new zone into the configuration file for a name which was already
configured as a member zone for a catalog zone. This has been fixed.
[GL #3911]
When named starts up, it sends a query for the DNSSEC key
for each configured trust anchor to determine whether the key has
changed. In some unusual cases, the query might depend on a zone for
which the server is itself authoritative, and would have failed if it
were sent before the zone was fully loaded. This has now been fixed by
delaying the key queries until all zones have finished loading.
[GL #3673]
A constant stream of zone additions and deletions via rndcreconfig could cause increased memory consumption due to delayed
cleaning of view memory. This has been fixed. [GL #3801]
The speed of the message digest algorithms (MD5, SHA-1, SHA-2), and of
NSEC3 hashing, has been improved. [GL #3795]
Building BIND 9 failed when the --enable-dnsrps switch for
./configure was used. This has been fixed. [GL #3827]
An UPDATE message flood could cause named to exhaust all
available memory. This flaw was addressed by adding a new
update-quota option that controls the maximum number of
outstanding DNS UPDATE messages that named can hold in a
queue at any given time (default: 100). (CVE-2022-3094)
ISC would like to thank Rob Schulhof from Infoblox for bringing this
vulnerability to our attention. [GL #3523]
named could crash with an assertion failure when an RRSIG
query was received and stale-answer-client-timeout was set to a
non-zero value. This has been fixed. (CVE-2022-3736)
ISC would like to thank Borja Marcos from Sarenet (with assistance by
Iratxe Niño from Fundación Sarenet) for bringing this vulnerability to
our attention. [GL #3622]
named running as a resolver with the
stale-answer-client-timeout option set to any value greater than
0 could crash with an assertion failure, when the
recursive-clients soft quota was reached. This has been fixed.
(CVE-2022-3924)
ISC would like to thank Maksym Odinintsev from AWS for bringing this
vulnerability to our attention. [GL #3619]
The new update-quota option can be used to control the number of
simultaneous DNS UPDATE messages that can be processed to update an
authoritative zone on a primary server, or forwarded to the primary
server by a secondary server. The default is 100. A new statistics
counter has also been added to record events when this quota is
exceeded, and the version numbers for the XML and JSON statistics
schemas have been updated. [GL #3523]
The Differentiated Services Code Point (DSCP) feature in BIND has been
deprecated. Configuring DSCP values in named.conf now causes a
warning to be logged. Note that this feature has only been partly
operational since the new Network Manager was introduced in BIND
9.16.0. [GL #3773]
The catalog zone implementation has been optimized to work with
hundreds of thousands of member zones. [GL #3744]
In certain query resolution scenarios (e.g. when following CNAME
records), named configured to answer from stale cache could
return a SERVFAIL response despite a usable, non-stale answer being
present in the cache. This has been fixed. [GL #3678]
When a catalog zone was removed from the configuration, in some cases
a dangling pointer could cause the named process to crash.
This has been fixed. [GL #3683]
When a zone was deleted from a server, a key management object related
to that zone was inadvertently kept in memory and only released upon
shutdown. This could lead to constantly increasing memory use on
servers with a high rate of changes affecting the set of zones being
served. This has been fixed. [GL #3727]
In certain cases, named waited for the resolution of
outstanding recursive queries to finish before shutting down. This was
unintended and has been fixed. [GL #3183]
The zone<name>/<class>:finalreferencedetached log message was
moved from the INFO log level to the DEBUG(1) log level to prevent the
named-checkzone tool from superfluously logging this message
in non-debug mode. [GL #3707]
A crash was fixed that happened when a dnssec-policy zone that
used NSEC3 was reconfigured to enable inline-signing. [GL #3591]
In certain resolution scenarios, quotas could be erroneously reached
for servers, including any configured forwarders, resulting in
SERVFAIL answers being sent to clients. This has been fixed.
[GL #3598]
rpz-ip rules in response-policy zones could be ineffective in
some cases if a query had the CD (Checking Disabled) bit set to 1.
This has been fixed. [GL #3247]
Previously, if Internet connectivity issues were experienced during
the initial startup of named, a BIND resolver with
dnssec-validation set to auto could enter into a state where
it would not recover without stopping named, manually
deleting the managed-keys.bind and managed-keys.bind.jnl
files, and starting named again. This has been fixed.
[GL #2895]
The statistics counter representing the current number of clients
awaiting recursive resolution results (RecursClients) could
overflow in certain resolution scenarios. This has been fixed.
[GL #3584]
Previously, BIND failed to start on Solaris-based systems with
hundreds of CPUs. This has been fixed. [GL #3563]
When a DNS resource record’s TTL value was equal to the resolver’s
configured prefetch “eligibility” value, the record was
erroneously not treated as eligible for prefetching. This has been
fixed. [GL #3603]
Previously, there was no limit to the number of database lookups
performed while processing large delegations, which could be abused to
severely impact the performance of named running as a
recursive resolver. This has been fixed. (CVE-2022-2795)
ISC would like to thank Yehuda Afek from Tel-Aviv University and Anat
Bremler-Barr & Shani Stajnrod from Reichman University for bringing
this vulnerability to our attention. [GL #3394]
named running as a resolver with the
stale-answer-client-timeout option set to 0 could crash with
an assertion failure, when there was a stale CNAME in the cache for
the incoming query. This has been fixed. (CVE-2022-3080) [GL #3517]
A memory leak was fixed that could be externally triggered in the
DNSSEC verification code for the ECDSA algorithm. (CVE-2022-38177)
[GL #3487]
Memory leaks were fixed that could be externally triggered in the
DNSSEC verification code for the EdDSA algorithm. (CVE-2022-38178)
[GL #3487]
Response Rate Limiting (RRL) code now treats all QNAMEs that are
subject to wildcard processing within a given zone as the same name,
to prevent circumventing the limits enforced by RRL. [GL #3459]
Zones using dnssec-policy now require dynamic DNS or
inline-signing to be configured explicitly. [GL #3381]
A backward-compatible approach was implemented for encoding
internationalized domain names (IDN) in dig and converting
the domain to IDNA2008 form; if that fails, BIND tries an IDNA2003
conversion. [GL #3485]
A serve-stale bug was fixed, where BIND would try to return stale data
from cache for lookups that received duplicate queries or queries that
would be dropped. This bug resulted in premature SERVFAIL responses,
and has now been resolved. [GL #2982]
The DNSSEC algorithms RSASHA1 and NSEC3RSASHA1 are now automatically
disabled on systems where they are disallowed by the security policy
(e.g. Red Hat Enterprise Linux 9). Primary zones using those
algorithms need to be migrated to new algorithms prior to running on
these systems, as graceful migration to different DNSSEC algorithms is
not possible when RSASHA1 is disallowed by the operating system.
[GL #3469]
Log messages related to fetch limiting have been improved to provide
more complete information. Specifically, the final counts of allowed
and spilled fetches are now logged before the counter object is
destroyed. [GL #3461]
Non-dynamic zones that inherit dnssec-policy from the
view or options blocks were not
marked as inline-signed and therefore never scheduled to be re-signed.
This has been fixed. [GL #3438]
The old max-zone-ttl zone option was meant to be superseded by
the max-zone-ttl option in dnssec-policy; however, the
latter option was not fully effective. This has been corrected: zones
no longer load if they contain TTLs greater than the limit configured
in dnssec-policy. For zones with both the old
max-zone-ttl option and dnssec-policy configured, the
old option is ignored, and a warning is generated. [GL #2918]
rndcdumpdb-expired was fixed to include
expired RRsets, even if stale-cache-enable is set to no and
the cache-cleaning time window has passed. [GL #3462]
An assertion failure caused by a TCP connection closing between a
connect (or accept) and a read from a socket has been fixed.
[GL #3400]
named could crash during a very rare situation that could
arise when validating a query which had timed out at that exact
moment. This has been fixed. [GL #3398]
The fetches-per-server quota is designed to adjust itself downward
automatically when an authoritative server times out too frequently.
Due to a coding error, that adjustment was applied incorrectly, so
that the quota for a congested server was always set to 1. This has
been fixed. [GL #3327]
DNSSEC-signed catalog zones were not being processed correctly. This
has been fixed. [GL #3380]
Key files were updated every time the dnssec-policy key manager
ran, whether the metadata had changed or not. named now
checks whether changes were applied before writing out the key files.
[GL #3302]
Previously, CDS and CDNSKEY DELETE records were removed from the zone
when configured with the auto-dnssecmaintain; option. This has
been fixed. [GL #2931]
Add a new configuration option reuseport to disable load balancing
on sockets in situations where processing of Response Policy Zones
(RPZ), Catalog Zones, or large zone transfers can cause service
disruptions. See the BIND 9 ARM for more detail. [GL #3249]
Invalid dnssec-policy definitions, where the defined keys did not
cover both KSK and ZSK roles for a given algorithm, were being
accepted. These are now checked, and the dnssec-policy is rejected
if both roles are not present for all algorithms in use. [GL #3142]
Handling of TCP write timeouts has been improved to track the timeout
for each TCP write separately, leading to a faster connection teardown
in case the other party is not reading the data. [GL #3200]
The rules for acceptance of records into the cache have been tightened
to prevent the possibility of poisoning if forwarders send records
outside the configured bailiwick. (CVE-2021-25220)
ISC would like to thank Xiang Li, Baojun Liu, and Chaoyi Lu from
Network and Information Security Lab, Tsinghua University, and
Changgen Zou from Qi An Xin Group Corp. for bringing this
vulnerability to our attention. [GL #2950]
TCP connections with keep-response-order enabled could leave the
TCP sockets in the CLOSE_WAIT state when the client did not
properly shut down the connection. (CVE-2022-0396) [GL #3112]
DEBUG(1)-level messages were added when starting and ending the BIND 9
task-exclusive mode that stops normal DNS operation (e.g. for
reconfiguration, interface scans, and other events that require
exclusive access to a shared resource). [GL #3137]
The max-transfer-time-out and max-transfer-idle-out options
were not implemented when the BIND 9 networking stack was refactored
in 9.16. The missing functionality has been re-implemented and
outgoing zone transfers now time out properly when not progressing.
[GL #1897]
TCP connections could hang indefinitely if the other party did not
read sent data, causing the TCP write buffers to fill. This has been
fixed by adding a “write” timer. Connections that are hung while
writing now time out after the tcp-idle-timeout period has
elapsed. [GL #3132]
The statistics counter representing the current number of clients
awaiting recursive resolution results (RecursClients) could be
miscalculated in certain resolution scenarios, potentially causing the
value of the counter to drop below zero. This has been fixed.
[GL #3147]
The DLZ API has been updated: EDNS Client-Subnet (ECS) options sent
by a client are now included in the client information sent to DLZ
modules when processing queries. [GL #3082]
Previously, recvmmsg support was enabled in libuv 1.35.0 and
1.36.0, but not in libuv versions 1.37.0 or greater, reducing the
maximum query-response performance. This has been fixed. [GL #3095]
A failed view configuration during a named reconfiguration
procedure could cause inconsistencies in BIND internal structures,
causing a crash or other unexpected errors. This has been fixed.
[GL #3060]
Previously, named logged a “quota reached” message when it hit its
hard quota on the number of connections. That message was accidentally
removed but has now been restored. [GL #3125]
Build errors were introduced in some DLZ modules due to an incomplete
change in the previous release. This has been fixed. [GL #3111]
Overall memory use by named has been optimized and reduced,
especially on systems with many CPU cores. The default memory
allocator has been switched from internal to external. A new
command-line option -Minternal allows named to be started
with the old internal memory allocator. [GL #2398]
On FreeBSD, TCP connections leaked a small amount of heap memory,
leading to an eventual out-of-memory problem. This has been fixed.
[GL #3051]
If signatures created by the ZSK were expired and the ZSK private key
was offline, the signatures were not replaced. This behavior has been
amended to replace the expired signatures with new signatures created
using the KSK. [GL #3049]
Under certain circumstances, the signed version of an inline-signed
zone could be dumped to disk without the serial number of the unsigned
version of the zone. This prevented resynchronization of the zone
contents after named restarted, if the unsigned zone file was
modified while named was not running. This has been fixed.
[GL #3071]
Previously, when an incoming TCP connection could not be accepted
because the client closed the connection early, an error message of
TCPconnectionfailed:socketisnotconnected was logged. This
message has been changed to AcceptingTCPconnectionfailed:socketisnotconnected. The severity level at which this type of message
is logged has also been changed from error to info for the
following triggering events: socketisnotconnected, quotareached, and softquotareached. [GL #2700]
dnssec-dsfromkey no longer generates DS records from revoked keys.
[GL #853]
Removing a configured catalog-zone clause from the configuration,
running rndcreconfig, then bringing back the removed
catalog-zone clause and running rndcreconfig again caused
named to crash. This has been fixed. [GL #1608]
Reloading a catalog zone which referenced a missing/deleted member
zone triggered a runtime check failure, causing named to exit
prematurely. This has been fixed. [GL #2308]
The lame-ttl option controls how long named caches certain
types of broken responses from authoritative servers (see the
security advisory for
details). This caching mechanism could be abused by an attacker to
significantly degrade resolver performance. The vulnerability has been
mitigated by changing the default value of lame-ttl to 0 and
overriding any explicitly set value with 0, effectively disabling
this mechanism altogether. ISC’s testing has determined that doing
that has a negligible impact on resolver performance while also
preventing abuse. Administrators may observe more traffic towards
servers issuing certain types of broken responses than in previous
BIND 9 releases, depending on client query patterns. (CVE-2021-25219)
ISC would like to thank Kishore Kumar Kothapalli of Infoblox for
bringing this vulnerability to our attention. [GL #2899]
The use of native PKCS#11 for Public-Key Cryptography in BIND 9 has
been deprecated in favor of the engine_pkcs11 OpenSSL engine from the
OpenSC project. The --with-native-pkcs11 configuration option
will be removed in the next major BIND 9 release. The option to use
the engine_pkcs11 OpenSSL engine is already available in BIND 9;
please see the ARM section on PKCS#11 for details.
[GL #2691]
Old-style Dynamically Loadable Zones (DLZ) drivers that had to be
enabled in named at build time have been marked as deprecated in
favor of new-style DLZ modules. Old-style DLZ drivers will be removed
in the next major BIND 9 release. [GL #2814]
The map zone file format has been marked as deprecated and will be
removed in the next major BIND 9 release. [GL #2882]
named and named-checkconf now exit with an error when a single
port configured for query-source, transfer-source,
notify-source, parental-source, and/or their respective IPv6
counterparts clashes with a global listening port. This configuration
has not been supported since BIND 9.16.0, but no error was reported
until now (even though sending UDP messages such as NOTIFY failed).
[GL #2888]
named and named-checkconf now issue a warning when there is a
single port configured for query-source, transfer-source,
notify-source, parental-source, and/or for their respective
IPv6 counterparts. [GL #2888]
A recent change introduced in BIND 9.16.21 inadvertently broke
backward compatibility for the check-namesmaster... and
check-namesslave... options, causing them to be silently
ignored. This has been fixed and these options now work properly
again. [GL #2911]
When new IP addresses were set up by the operating system during
named startup, it could fail to listen for TCP connections on the
newly added interfaces. [GL #2852]
Support for HTTPS and SVCB record types has been added. (This does not
include ADDITIONAL section processing for these record types, only
basic support for RR type parsing and printing.) [GL #1132]
When dnssec-signzone signs a zone using a successor key whose
predecessor is still published, it now only refreshes signatures for
RRsets which have an invalid signature, an expired signature, or a
signature which expires within the provided cycle interval. This
allows dnssec-signzone to gradually replace signatures in a zone
whose ZSK is being rolled over (similarly to what auto-dnssecmaintain; does). [GL #1551]
A recent change to the internal memory structure of zone databases
inadvertently neglected to update the MAPAPI value for zone files in
map format. This caused version 9.16.20 of named to attempt to
load files into memory that were no longer compatible, triggering an
assertion failure on startup. The MAPAPI value has now been updated,
so named rejects outdated files when encountering them.
[GL #2872]
Zone files in map format whose size exceeded 2 GB failed to load.
This has been fixed. [GL #2878]
named was unable to run as a Windows Service under certain
circumstances. This has been fixed. [GL #2837]
Stale data in the cache could cause named to send non-minimized
queries despite QNAME minimization being enabled. This has been fixed.
[GL #2665]
When a DNSSEC-signed zone which only has a single signing key
available is migrated to dnssec-policy, that key is now treated as
a Combined Signing Key (CSK). [GL #2857]
When a dynamic zone was made available in another view using the
in-view statement, running rndcfreeze always reported an
alreadyfrozen error even though the zone was successfully
frozen. This has been fixed. [GL #2844]
Fixed an assertion failure that occurred in named when it
attempted to send a UDP packet that exceeded the MTU size, if
Response Rate Limiting (RRL) was enabled. (CVE-2021-25218) [GL #2856]
named failed to check the opcode of responses when performing zone
refreshes, stub zone updates, and UPDATE forwarding. This could lead
to an assertion failure under certain conditions and has been
addressed by rejecting responses whose opcode does not match the
expected value. [GL #2762]
Testing revealed that setting the thread affinity for various types of
named threads led to inconsistent recursive performance, as
sometimes multiple sets of threads competed over a single resource.
Due to the above, named no longer sets thread affinity. This
causes a slight dip of around 5% in authoritative performance, but
recursive performance is now consistently improved. [GL #2822]
CDS and CDNSKEY records can now be published in a zone without the
requirement that they exactly match an existing DNSKEY record, as long
as the zone is signed with an algorithm represented in the CDS or
CDNSKEY record. This allows a clean rollover from one DNS provider to
another when using a multiple-signer DNSSEC configuration. [GL #2710]
Authentication of rndc messages could fail if a controls
statement was configured with multiple key algorithms for the same
listener. This has been fixed. [GL #2756]
Using a new configuration option, parental-agents, each zone can
now be associated with a list of servers that can be used to check the
DS RRset in the parent zone. This enables automatic KSK rollovers.
[GL #1126]
IP fragmentation has been disabled for outgoing UDP sockets. Errors
triggered by sending DNS messages larger than the specified path MTU
are properly handled by sending empty DNS replies with the TC
(TrunCated) bit set, which forces DNS clients to fall back to TCP.
[GL #2790]
The code managing RFC 5011 trust anchors created an invalid
placeholder keydata record upon a refresh failure, which prevented the
database of managed keys from subsequently being read back. This has
been fixed. [GL #2686]
Signed, insecure delegation responses prepared by named either
lacked the necessary NSEC records or contained duplicate NSEC records
when both wildcard expansion and CNAME chaining were required to
prepare the response. This has been fixed. [GL #2759]
If nsupdate sends an SOA request and receives a REFUSED response,
it now fails over to the next available server. [GL #2758]
A bug that caused the NSEC3 salt to be changed on every restart for
zones using KASP has been fixed. [GL #2725]
The configuration-checking code failed to account for the inheritance
rules of the dnssec-policy option. This has been fixed.
[GL #2780]
The fix for [GL #1875] inadvertently introduced a deadlock: when
locking key files for reading and writing, the in-view logic was
not considered. This has been fixed. [GL #2783]
A race condition could occur where two threads were competing for the
same set of key file locks, leading to a deadlock. This has been
fixed. [GL #2786]
When preparing DNS responses, named could replace the letters
W (uppercase) and w (lowercase) with \000. This has been
fixed. [GL #2779]
The configuration-checking code failed to account for the inheritance
rules of the key-directory option. As a side effect of this flaw,
the code detecting key-directory conflicts for zones using KASP
incorrectly reported unique key directories as being reused. This has
been fixed. [GL #2778]
After the network manager was introduced to named to handle
incoming traffic, it was discovered that recursive performance had
degraded compared to previous BIND 9 versions. This has now been
fixed by processing internal tasks inside network manager worker
threads, preventing resource contention among two sets of threads.
[GL #2638]
Zone dumping tasks are now run on separate asynchronous thread pools.
This change prevents zone dumping from blocking network I/O.
[GL #2732]
inline-signing was incorrectly described as being inherited from
the options/view levels and was incorrectly accepted at those
levels without effect. This has been fixed; named.conf files with
inline-signing at those levels no longer load. [GL #2536]
The calculation of the estimated IXFR transaction size in
dns_journal_iter_init() was invalid. This resulted in excessive
AXFR-style IXFR responses. [GL #2685]
Fixed an assertion failure that could occur if stale data was used to
answer a query, and then a prefetch was triggered after the query was
restarted (for example, to follow a CNAME). [GL #2733]
If a query was answered with stale data on a server with DNS64
enabled, an assertion could occur if a non-stale answer arrived
afterward. This has been fixed. [GL #2731]
Fixed an error which caused the IP_DONTFRAG socket option to be
enabled instead of disabled, leading to errors when sending oversized
UDP packets. [GL #2746]
Zones which are configured in multiple views, with different values
set for dnssec-policy and with identical values set for
key-directory, are now detected and treated as a configuration
error. [GL #2463]
A race condition could occur when reading and writing key files for
zones using KASP and configured in multiple views. This has been
fixed. [GL #1875]
DNSSEC responses containing NSEC3 records with iteration counts
greater than 150 are now treated as insecure. [GL #2445]
The maximum supported number of NSEC3 iterations that can be
configured for a zone has been reduced to 150. [GL #2642]
The default value of the max-ixfr-ratio option was changed to
unlimited, for better backwards compatibility in the stable
release series. [GL #2671]
Zones that want to transition from secure to insecure mode without
becoming bogus in the process must now have their dnssec-policy
changed first to insecure, rather than none. After the DNSSEC
records have been removed from the zone, the dnssec-policy can be
set to none or removed from the configuration. Setting the
dnssec-policy to insecure causes CDS and CDNSKEY DELETE
records to be published. [GL #2645]
The implementation of the ZONEMD RR type has been updated to match
RFC 8976. [GL #2658]
The draft-vandijk-dnsop-nsec-ttl IETF draft was implemented:
NSEC(3) TTL values are now set to the minimum of the SOA MINIMUM value
or the SOA TTL. [GL #2347]
It was possible for corrupt journal files generated by an earlier
version of named to cause problems after an upgrade. This has been
fixed. [GL #2670]
TTL values in cache dumps were reported incorrectly when
stale-cache-enable was set to yes. This has been fixed.
[GL #389][GL #2289]
A deadlock could occur when multiple rndcaddzone, rndcdelzone, and/or rndcmodzone commands were invoked
simultaneously for different zones. This has been fixed. [GL #2626]
named and named-checkconf did not report an error when
multiple zones with the dnssec-policy option set were using the
same zone file. This has been fixed. [GL #2603]
If dnssec-policy was active and a private key file was temporarily
offline during a rekey event, named could incorrectly introduce
replacement keys and break a signed zone. This has been fixed.
[GL #2596]
When generating zone signing keys, KASP now also checks for key ID
conflicts among newly created keys, rather than just between new and
existing ones. [GL #2628]
A malformed incoming IXFR transfer could trigger an assertion failure
in named, causing it to quit abnormally. (CVE-2021-25214)
ISC would like to thank Greg Kuechle of SaskTel for bringing this
vulnerability to our attention. [GL #2467]
named crashed when a DNAME record placed in the ANSWER section
during DNAME chasing turned out to be the final answer to a client
query. (CVE-2021-25215)
ISC would like to thank Siva Kakarla for bringing this
vulnerability to our attention. [GL #2540]
When a server’s configuration set the tkey-gssapi-keytab or
tkey-gssapi-credential option, a specially crafted GSS-TSIG query
could cause a buffer overflow in the ISC implementation of SPNEGO (a
protocol enabling negotiation of the security mechanism used for
GSSAPI authentication). This flaw could be exploited to crash
named binaries compiled for 64-bit platforms, and could enable
remote code execution when named was compiled for 32-bit
platforms. (CVE-2021-25216)
This vulnerability was reported to us as ZDI-CAN-13347 by Trend Micro
Zero Day Initiative. [GL #2604]
The ISC implementation of SPNEGO was removed from BIND 9 source code.
Instead, BIND 9 now always uses the SPNEGO implementation provided by
the system GSSAPI library when it is built with GSSAPI support. All
major contemporary Kerberos/GSSAPI libraries contain an implementation
of the SPNEGO mechanism. [GL #2607]
The default value for the stale-answer-client-timeout option was
changed from 1800 (ms) to off. The default value may be
changed again in future releases as this feature matures. [GL #2608]
TCP idle and initial timeouts were being incorrectly applied: only the
tcp-initial-timeout was applied on the whole connection, even if
the connection were still active, which could prevent a large zone
transfer from being sent back to the client. The default setting for
tcp-initial-timeout was 30 seconds, which meant that any TCP
connection taking more than 30 seconds was abruptly terminated. This
has been fixed. [GL #2583]
When stale-answer-client-timeout was set to a positive value and
recursion for a client query completed when named was about to
look for a stale answer, an assertion could fail in
query_respond(), resulting in a crash. This has been fixed.
[GL #2594]
If zone journal files written by BIND 9.16.11 or earlier were present
when BIND was upgraded to BIND 9.16.13 or BIND 9.16.14, the zone file
for that zone could have been inadvertently rewritten with the current
zone contents. This caused the original zone file structure (e.g.
comments, $INCLUDE directives) to be lost, although the zone data
itself was preserved. [GL #2623]
After upgrading to BIND 9.16.13, journal files for trust anchor
databases (e.g. managed-keys.bind.jnl) could be left in a corrupt
state. (Other zone journal files were not affected.) This has been
fixed. If a corrupt journal file is detected, named can now
recover from it. [GL #2600]
When sending queries over TCP, dig now properly handles +tries=1+retry=0 by not retrying the connection when the remote server
closes the connection prematurely. [GL #2490]
CDS/CDNSKEY DELETE records are now removed when a zone transitions
from a secure to an insecure state. named-checkzone also no longer
reports an error when such records are found in an unsigned zone.
[GL #2517]
Zones using KASP could not be thawed after they were frozen using
rndcfreeze. This has been fixed. [GL #2523]
After rndccheckds-checkds or rndcdnssec-rollover is used,
named now immediately attempts to reconfigure zone keys. This
change prevents unnecessary key rollover delays. [GL #2488]
Previously, a memory leak could occur when named failed to bind a
UDP socket to a network interface. This has been fixed. [GL #2575]
The BIND 9.16.14 release was withdrawn after a backporting bug was
discovered during pre-release testing. ISC would like to acknowledge
the assistance of Natan Segal of Bluecat Networks.
A new purge-keys option has been added to dnssec-policy. It
sets the period of time that key files are retained after becoming
obsolete due to a key rollover; the default is 90 days. This feature
can be disabled by setting purge-keys to 0. [GL #2408]
When serve-stale is enabled and stale data is available, named now
returns stale answers upon encountering any unexpected error in the
query resolution process. This may happen, for example, if the
fetches-per-server or fetches-per-zone limits are reached. In
this case, named attempts to answer DNS requests with stale data,
but does not start the stale-refresh-time window. [GL #2434]
Zone journal (.jnl) files created by versions of named prior
to 9.16.12 were no longer compatible; this could cause problems when
upgrading if journal files were not synchronized first. This has been
corrected: older journal files can now be read when starting up. When
an old-style journal file is detected, it is updated to the new format
immediately after loading.
Note that journals created by the current version of named are not
usable by versions prior to 9.16.12. Before downgrading to a prior
release, users are advised to ensure that all dynamic zones have been
synchronized using rndcsync-clean.
A journal file’s format can be changed manually by running
named-journalprint-d (downgrade) or named-journalprint-u
(upgrade). Note that this must not be done while named is
running. [GL #2505]
named crashed when it was allowed to serve stale answers and
stale-answer-client-timeout was triggered without any (stale) data
available in the cache to answer the query. [GL #2503]
If an outgoing packet exceeded max-udp-size, named dropped it
instead of sending back a proper response. To prevent this problem,
the IP_DONTFRAG option is no longer set on UDP sockets, which has
been happening since BIND 9.16.11. [GL #2466]
NSEC3 records were not immediately created when signing a dynamic zone
using dnssec-policy with nsec3param. This has been fixed.
[GL #2498]
A memory leak occurred when named was reconfigured after adding an
inline-signed zone with auto-dnssecmaintain enabled. This has
been fixed. [GL #2041]
An invalid direction field (not one of N, S, E, W) in
a LOC record resulted in an INSIST failure when a zone file containing
such a record was loaded. [GL #2499]
When tkey-gssapi-keytab or tkey-gssapi-credential was
configured, a specially crafted GSS-TSIG query could cause a buffer
overflow in the ISC implementation of SPNEGO (a protocol enabling
negotiation of the security mechanism to use for GSSAPI
authentication). This flaw could be exploited to crash named.
Theoretically, it also enabled remote code execution, but achieving
the latter is very difficult in real-world conditions.
(CVE-2020-8625)
This vulnerability was responsibly reported to us as ZDI-CAN-12302 by
Trend Micro Zero Day Initiative. [GL #2354]
When a secondary server receives a large incremental zone transfer
(IXFR), it can have a negative impact on query performance while the
incremental changes are applied to the zone. To address this,
named can now limit the size of IXFR responses it sends in
response to zone transfer requests. If an IXFR response would be
larger than an AXFR of the entire zone, it will send an AXFR response
instead.
This behavior is controlled by the max-ixfr-ratio option - a
percentage value representing the ratio of IXFR size to the size of a
full zone transfer. The default is 100%. [GL #1515]
A new option, stale-answer-client-timeout, has been added to
improve named’s behavior with respect to serving stale data. The
option defines the amount of time named waits before attempting to
answer the query with a stale RRset from cache. If a stale answer is
found, named continues the ongoing fetches, attempting to refresh
the RRset in cache until the resolver-query-timeout interval is
reached.
The default value is 1800 (in milliseconds) and the maximum value
is limited to resolver-query-timeout minus one second. A value of
0 causes any available cached RRset to immediately be returned
while still triggering a refresh of the data in cache.
This new behavior can be disabled by setting
stale-answer-client-timeout to off or disabled. The new
option has no effect if stale-answer-enable is disabled.
[GL #2247]
As part of an ongoing effort to use RFC 8499 terminology,
primaries can now be used as a synonym for masters in
named.conf. Similarly, notifyprimary-only can now be used as
a synonym for notifymaster-only. The output of rndczonestatus now uses primary and secondary terminology.
[GL #1948]
The default value of max-stale-ttl has been changed from 12 hours
to 1 day and the default value of stale-answer-ttl has been
changed from 1 second to 30 seconds, following RFC 8767
recommendations. [GL #2248]
The SONAMEs for BIND 9 libraries now include the current BIND 9
version number, in an effort to tightly couple internal libraries with
a specific release. This change makes the BIND 9 release process both
simpler and more consistent while also unequivocally preventing BIND 9
binaries from silently loading wrong versions of shared libraries (or
multiple versions of the same shared library) at startup. [GL #2387]
When check-names is in effect, A records below an _spf,
_spf_rate, or _spf_verify label (which are employed by the
exists SPF mechanism defined in RFC 7208 section 5.7/appendix
D.1) are no longer reported as warnings/errors. [GL #2377]
named failed to start when its configuration included a zone with
a non-builtin allow-update ACL attached. [GL #2413]
Previously, dnssec-keyfromlabel crashed when operating on an ECDSA
key. This has been fixed. [GL #2178]
KASP incorrectly set signature validity to the value of the DNSKEY
signature validity. This has been fixed. [GL #2383]
When migrating to KASP, BIND 9 considered keys with the Inactive
and/or Delete timing metadata to be possible active keys. This has
been fixed. [GL #2406]
Fix the “three is a crowd” key rollover bug in KASP. When keys rolled
faster than the time required to finish the rollover procedure, the
successor relation equation failed because it assumed only two keys
were taking part in a rollover. This could lead to premature removal
of predecessor keys. BIND 9 now implements a recursive successor
relation, as described in the paper “Flexible and Robust Key Rollover”
(Equation (2)). [GL #2375]
Performance of the DNSSEC verification code (used by
dnssec-signzone, dnssec-verify, and mirror zones) has been
improved. [GL #2073]
The new networking code introduced in BIND 9.16 (netmgr) was
overhauled in order to make it more stable, testable, and
maintainable. [GL #2321]
Earlier releases of BIND versions 9.16 and newer required the
operating system to support load-balanced sockets in order for
named to be able to achieve high performance (by distributing
incoming queries among multiple threads). However, the only operating
systems currently known to support load-balanced sockets are Linux and
FreeBSD 12, which means both UDP and TCP performance were limited to a
single thread on other systems. As of BIND 9.16.11, named attempts
to distribute incoming queries among multiple threads on systems which
lack support for load-balanced sockets (except Windows). [GL #2137]
It is now possible to transition a zone from secure to insecure mode
without making it bogus in the process; changing to dnssec-policynone; also causes CDS and CDNSKEY DELETE records to be published, to
signal that the entire DS RRset at the parent must be removed, as
described in RFC 8078. [GL #1750]
When using the unixtime or date method to update the SOA
serial number, named and dnssec-signzone silently fell back to
the increment method to prevent the new serial number from being
smaller than the old serial number (using serial number arithmetics).
dnssec-signzone now prints a warning message, and named logs a
warning, when such a fallback happens. [GL #2058]
Multiple threads could attempt to destroy a single RBTDB instance at
the same time, resulting in an unpredictable but low-probability
assertion failure in free_rbtdb(). This has been fixed.
[GL #2317]
named no longer attempts to assign threads to CPUs outside the CPU
affinity set. Thanks to Ole Bjørn Hessen. [GL #2245]
When reconfiguring named, removing auto-dnssec did not turn
off DNSSEC maintenance. This has been fixed. [GL #2341]
The report of intermittent BIND assertion failures triggered in
lib/dns/resolver.c:dns_name_issubdomain() has now been closed
without further action. Our initial response to this was to add
diagnostic logging instead of terminating named, anticipating that
we would receive further useful troubleshooting input. This workaround
first appeared in BIND releases 9.17.5 and 9.16.7. However, since
those releases were published, there have been no new reports of
assertion failures matching this issue, but also no further diagnostic
input, so we have closed the issue. [GL #2091]
NSEC3 support was added to KASP. A new option for dnssec-policy,
nsec3param, can be used to set the desired NSEC3 parameters.
NSEC3 salt collisions are automatically prevented during resalting.
[GL #1620]
The default value of max-recursion-queries was increased from 75
to 100. Since the queries sent towards root and TLD servers are now
included in the count (as a result of the fix for CVE-2020-8616),
max-recursion-queries has a higher chance of being exceeded by
non-attack queries, which is the main reason for increasing its
default value. [GL #2305]
The default value of nocookie-udp-size was restored back to 4096
bytes. Since max-udp-size is the upper bound for
nocookie-udp-size, this change relieves the operator from having
to change nocookie-udp-size together with max-udp-size in
order to increase the default EDNS buffer size limit.
nocookie-udp-size can still be set to a value lower than
max-udp-size, if desired. [GL #2250]
A new configuration option, stale-refresh-time, has been
introduced. It allows a stale RRset to be served directly from cache
for a period of time after a failed lookup, before a new attempt to
refresh it is made. [GL #2066]
named could crash with an assertion failure if a TCP connection
were closed while a request was still being processed. [GL #2227]
named acting as a resolver could incorrectly treat signed zones
with no DS record at the parent as bogus. Such zones should be treated
as insecure. This has been fixed. [GL #2236]
After a Negative Trust Anchor (NTA) is added, BIND performs periodic
checks to see if it is still necessary. If BIND encountered a failure
while creating a query to perform such a check, it attempted to
dereference a NULL pointer, resulting in a crash. [GL #2244]
A problem obtaining glue records could prevent a stub zone from
functioning properly, if the authoritative server for the zone were
configured for minimal responses. [GL #1736]
UV_EOF is no longer treated as a TCP4RecvErr or a
TCP6RecvErr. [GL #2208]
Add a new rndc command, rndcdnssec-rollover, which triggers
a manual rollover for a specific key. [GL #1749]
Add a new rndc command, rndcdumpdb-expired, which dumps the
cache database, including expired RRsets that are awaiting cleanup, to
the dump-file for diagnostic purposes. [GL #1870]
DNS Flag Day 2020: The default EDNS buffer size has been changed from
4096 to 1232 bytes. According to measurements done by multiple
parties, this should not cause any operational problems as most of the
Internet “core” is able to cope with IP message sizes between
1400-1500 bytes; the 1232 size was picked as a conservative minimal
number that could be changed by the DNS operator to an estimated path
MTU minus the estimated header space. In practice, the smallest MTU
witnessed in the operational DNS community is 1500 octets, the maximum
Ethernet payload size, so a useful default for maximum DNS/UDP payload
size on reliable networks would be 1432 bytes. [GL #2183]
named reported an invalid memory size when running in an
environment that did not properly report the number of available
memory pages and/or the size of each memory page. [GL #2166]
With multiple forwarders configured, named could fail the
REQUIRE(msg->state==(-1)) assertion in lib/dns/message.c,
causing it to crash. This has been fixed. [GL #2124]
named erroneously performed continuous key rollovers for KASP
policies that used algorithm Ed25519 or Ed448 due to a mismatch
between created key size and expected key size. [GL #2171]
Updating contents of an RPZ zone which contained names spelled using
varying letter case could cause some processing rules in that RPZ zone
to be erroneously ignored. [GL #2169]
Add a new rndc command, rndcdnssec-checkds, which signals to
named that a DS record for a given zone or key has been published
or withdrawn from the parent. This command replaces the time-based
parent-registration-delay configuration option. [GL #1613]
Log when named adds a CDS/CDNSKEY to the zone. [GL #1748]
In rare circumstances, named would exit with an assertion failure
when the number of nodes stored in the red-black tree exceeded the
maximum allowed size of the internal hash table. [GL #2104]
Silence spurious system log messages for an EPROTO(71) error code that
was seen on older operating systems, where unhandled ICMPv6 errors
resulted in a generic protocol error being returned instead of a more
specific error code. [GL #1928]
With query name minimization enabled, named failed to resolve
ip6.arpa. names that had extra labels to the left of the IPv6
part. For example, when named attempted query name minimization on
a name like A.B.1.2.3.4.(...).ip6.arpa., it stopped at the
leftmost IPv6 label, i.e. 1.2.3.4.(...).ip6.arpa., without
considering the extra labels (A.B). That caused a query loop when
resolving the name: if named received NXDOMAIN answers, then the
same query was repeatedly sent until the number of queries sent
reached the value of the max-recursion-queries configuration
option. [GL #1847]
Parsing of LOC records was made more strict by rejecting a sole period
(.) and/or m as a value. These changes prevent zone files
using such values from being loaded. Handling of negative altitudes
which are not integers was also corrected. [GL #2074]
It was possible to trigger an assertion failure by sending a specially
crafted large TCP DNS message. This was disclosed in CVE-2020-8620.
ISC would like to thank Emanuel Almeida of Cisco Systems, Inc. for
bringing this vulnerability to our attention. [GL #1996]
named could crash after failing an assertion check in certain
query resolution scenarios where QNAME minimization and forwarding
were both enabled. To prevent such crashes, QNAME minimization is now
always disabled for a given query resolution process, if forwarders
are used at any point. This was disclosed in CVE-2020-8621.
ISC would like to thank Joseph Gullo for bringing this vulnerability
to our attention. [GL #1997]
It was possible to trigger an assertion failure when verifying the
response to a TSIG-signed request. This was disclosed in
CVE-2020-8622.
ISC would like to thank Dave Feldman, Jeff Warren, and Joel Cunningham
of Oracle for bringing this vulnerability to our attention.
[GL #2028]
When BIND 9 was compiled with native PKCS#11 support, it was possible
to trigger an assertion failure in code determining the number of bits
in the PKCS#11 RSA public key with a specially crafted packet. This
was disclosed in CVE-2020-8623.
ISC would like to thank Lyu Chiy for bringing this vulnerability to
our attention. [GL #2037]
update-policy rules of type subdomain were incorrectly treated
as zonesub rules, which allowed keys used in subdomain rules
to update names outside of the specified subdomains. The problem was
fixed by making sure subdomain rules are again processed as
described in the ARM. This was disclosed in CVE-2020-8624.
ISC would like to thank Joop Boonen of credativ GmbH for bringing this
vulnerability to our attention. [GL #2055]
BIND’s cache database implementation has been updated to use a faster
hash function with better distribution. In addition, the effective
max-cache-size (configured explicitly, defaulting to a value based
on system memory or set to unlimited) now pre-allocates fixed-size
hash tables. This prevents interruption to query resolution when the
hash table sizes need to be increased. [GL #1775]
Resource records received with 0 TTL are no longer kept in the cache
to be used for stale answers. [GL #1829]
Wildcard RPZ passthru rules could incorrectly be overridden by other
rules that were loaded from RPZ zones which appeared later in the
response-policy statement. This has been fixed. [GL #1619]
The IPv6 Duplicate Address Detection (DAD) mechanism could
inadvertently prevent named from binding to new IPv6 interfaces,
by causing multiple route socket messages to be sent for each IPv6
address. named monitors for new interfaces to bind() to when
it is configured to listen on any or on a specific range of
addresses. New IPv6 interfaces can be in a “tentative” state before
they are fully available for use. When DAD is in use, two messages are
emitted by the route socket: one when the interface first appears and
then a second one when it is fully “up.” An attempt by named to
bind() to the new interface prematurely would fail, causing it
thereafter to ignore that address/interface. The problem was worked
around by setting the IP_FREEBIND option on the socket and trying
to bind() to each IPv6 address again if the first bind() call
for that address failed with EADDRNOTAVAIL. [GL #2038]
Addressed an error in recursive clients stats reporting which could
cause underflow, and even negative statistics. There were occasions
when an incoming query could trigger a prefetch for some eligible
RRset, and if the prefetch code were executed before recursion, no
increment in recursive clients stats would take place. Conversely,
when processing the answers, if the recursion code were executed
before the prefetch, the same counter would be decremented without a
matching increment. [GL #1719]
The introduction of KASP support inadvertently caused the second field
of sig-validity-interval to always be calculated in hours, even in
cases when it should have been calculated in days. This has been
fixed. (Thanks to Tony Finch.) [GL !3735]
LMDB locking code was revised to make rndcreconfig work properly
on FreeBSD and with LMDB >= 0.9.26. [GL #1976]
A race condition could occur if a TCP socket connection was closed
while named was waiting for a recursive response. The attempt to
send a response over the closing connection triggered an assertion
failure in the function isc__nm_tcpdns_send(). [GL #1937]
A race condition could occur when named attempted to use a UDP
interface that was shutting down. This triggered an assertion failure
in uv__udp_finish_close(). [GL #1938]
Fix assertion failure when server was under load and root zone had not
yet been loaded. [GL #1862]
named could crash when cleaning dead nodes in lib/dns/rbtdb.c
that were being reused. [GL #1968]
named crashed on shutdown when a new rndc connection was
received during shutdown. This has been fixed. [GL #1747]
The DS RRset returned by dns_keynode_dsset() was used in a
non-thread-safe manner. This could result in an INSIST being
triggered. [GL #1926]
Properly handle missing kyua command so that makecheck does
not fail unexpectedly when CMocka is installed, but Kyua is not.
[GL #1950]
The primary and secondary keywords, when used as parameters
for check-names, were not processed correctly and were being
ignored. [GL #1949]
rndcdnstap-roll<value> did not limit the number of saved files
to <value>. [GL !3728]
The validator could fail to accept a properly signed RRset if an
unsupported algorithm appeared earlier in the DNSKEY RRset than a
supported algorithm. It could also stop if it detected a malformed
public key. [GL #1689]
The blackhole ACL was inadvertently disabled for client queries.
Blocked IP addresses were not used for upstream queries but queries
from those addresses could still be answered. [GL #1936]
It was possible to trigger an assertion when attempting to fill an
oversized TCP buffer. This was disclosed in CVE-2020-8618.
[GL #1850]
It was possible to trigger an INSIST failure when a zone with an
interior wildcard label was queried in a certain pattern. This was
disclosed in CVE-2020-8619. [GL #1111][GL #1718]
Documentation was converted from DocBook to reStructuredText. The
BIND 9 ARM is now generated using Sphinx and published on Read the
Docs. Release notes are no longer available as a separate document
accompanying a release. [GL #83]
named and named-checkzone now reject master zones that have a
DS RRset at the zone apex. Attempts to add DS records at the zone
apex via UPDATE will be logged but otherwise ignored. DS records
belong in the parent zone, not at the zone apex. [GL #1798]
dig and other tools can now print the Extended DNS Error (EDE)
option when it appears in a request or a response. [GL #1835]
The default value of max-stale-ttl has changed from 1 week to 12
hours. This option controls how long named retains expired RRsets
in cache as a potential mitigation mechanism, should there be a
problem with one or more domains. Note that cache content retention
is independent of whether stale answers are used in response to
client queries (stale-answer-enableyes|no and rndcserve-staleon|off). Serving of stale answers when the authoritative servers
are not responding must be explicitly enabled, whereas the retention
of expired cache content takes place automatically on all versions of
BIND 9 that have this feature available. [GL #1877]
Warning
This change may be significant for administrators who expect that
stale cache content will be automatically retained for up to 1
week. Add option max-stale-ttl1w; to named.conf to keep
the previous behavior of named.
listen-on-v6{any;} creates a separate socket for each
interface. Previously, just one socket was created on systems
conforming to RFC 3493 and RFC 3542. This change was introduced
in BIND 9.16.0, but it was accidentally omitted from documentation.
[GL #1782]
When fully updating the NSEC3 chain for a large zone via IXFR, a
temporary loss of performance could be experienced on the secondary
server when answering queries for nonexistent data that required
DNSSEC proof of non-existence (in other words, queries that required
the server to find and to return NSEC3 data). The unnecessary
processing step that was causing this delay has now been removed.
[GL #1834]
named could crash with an assertion failure if the name of a
database node was looked up while the database was being modified.
[GL #1857]
A possible deadlock in lib/isc/unix/socket.c was fixed.
[GL #1859]
Previously, named did not destroy some mutexes and conditional
variables in netmgr code, which caused a memory leak on FreeBSD. This
has been fixed. [GL #1893]
A data race in lib/dns/resolver.c:log_formerr() that could lead
to an assertion failure was fixed. [GL #1808]
Previously, provide-ixfrno; failed to return up-to-date
responses when the serial number was greater than or equal to the
current serial number. [GL #1714]
A bug in dnssec-policy keymgr was fixed, where the check for the
existence of a given key’s successor would incorrectly return
true if any other key in the keyring had a successor. [GL #1845]
With dnssec-policy, when creating a successor key, the “goal” state
of the current active key (the predecessor) was not changed and thus
never removed from the zone. [GL #1846]
named-checkconf-p could include spurious text in
server-addresses statements due to an uninitialized DSCP value.
This has been fixed. [GL #1812]
The ARM has been updated to indicate that the TSIG session key is
generated when named starts, regardless of whether it is needed.
[GL #1842]
To prevent exhaustion of server resources by a maliciously configured
domain, the number of recursive queries that can be triggered by a
request before aborting recursion has been further limited. Root and
top-level domain servers are no longer exempt from the
max-recursion-queries limit. Fetches for missing name server
address records are limited to 4 for any domain. This issue was
disclosed in CVE-2020-8616. [GL #1388]
Replaying a TSIG BADTIME response as a request could trigger an
assertion failure. This was disclosed in CVE-2020-8617. [GL #1703]
BIND crashes on startup when linked against libuv 1.36. This issue
is related to recvmmsg() support in libuv, which was first
included in libuv 1.35. The problem was addressed in libuv 1.37, but
the relevant libuv code change requires a special flag to be set
during library initialization in order for recvmmsg() support to
be enabled. This BIND release sets that special flag when required,
so recvmmsg() support is now enabled when BIND is compiled
against either libuv 1.35 or libuv 1.37+; libuv 1.36 is still not
usable with BIND. [GL #1761][GL #1797]
See above for a list of all known
issues affecting this BIND 9 branch.
BIND 9 no longer sets receive/send buffer sizes for UDP sockets,
relying on system defaults instead. [GL #1713]
The default rwlock implementation has been changed back to the native
BIND 9 rwlock implementation. [GL #1753]
The native PKCS#11 EdDSA implementation has been updated to PKCS#11
v3.0 and thus made operational again. Contributed by Aaron Thompson.
[GL !3326]
The OpenSSL ECDSA implementation has been updated to support PKCS#11
via OpenSSL engine (see engine_pkcs11 from libp11 project).
[GL #1534]
The OpenSSL EdDSA implementation has been updated to support PKCS#11
via OpenSSL engine. Please note that an EdDSA-capable OpenSSL engine
is required and thus this code is only a proof-of-concept for the
time being. Contributed by Aaron Thompson. [GL #1763]
Message IDs in inbound AXFR transfers are now checked for
consistency. Log messages are emitted for streams with inconsistent
message IDs. [GL #1674]
The zone timers are now exported to the statistics channel. For the
primary zones, only the loaded time is exported. For the secondary
zones, the exported timers also include expire and refresh times.
Contributed by Paul Frieden, Verizon Media. [GL #1232]
A bug in dnstap initialization could prevent some dnstap data from
being logged, especially on recursive resolvers. [GL #1795]
When running on a system with support for Linux capabilities,
named drops root privileges very soon after system startup. This
was causing a spurious log message, unabletoseteffectiveuidto0:Operationnotpermitted, which has now been silenced.
[GL #1042][GL #1090]
When named-checkconf-z was run, it would sometimes incorrectly set
its exit code. It reflected only the status of the last view found;
any errors found for other configured views were not reported. Thanks
to Graham Clinch. [GL #1807]
When built without LMDB support, named failed to restart after a
zone with a double quote (”) in its name was added with
rndcaddzone. Thanks to Alberto Fernández. [GL #1695]
DNS rebinding protection was ineffective when BIND 9 is configured as
a forwarding DNS server. Found and responsibly reported by Tobias
Klein. [GL #1574]
We have received reports that in some circumstances, receipt of an
IXFR can cause the processing of queries to slow significantly. Some
of these were related to RPZ processing, which has been fixed in this
release (see below). Others appear to occur where there are
NSEC3-related changes (such as an operator changing the NSEC3 salt
used in the hash calculation). These are being investigated.
[GL #1685]
See above for a list of all known
issues affecting this BIND 9 branch.
The previous DNSSEC sign statistics used lots of memory. The number
of keys to track is reduced to four per zone, which should be enough
for 99% of all signed zones. [GL #1179]
When an RPZ policy zone was updated via zone transfer and a large
number of records was deleted, named could become nonresponsive
for a short period while deleted names were removed from the RPZ
summary database. This database cleanup is now done incrementally
over a longer period of time, reducing such delays. [GL #1447]
When trying to migrate an already-signed zone from
auto-dnssecmaintain to one based on dnssec-policy, the
existing keys were immediately deleted and replaced with new ones. As
the key rollover timing constraints were not being followed, it was
possible that some clients would not have been able to validate
responses until all old DNSSEC information had timed out from caches.
BIND now looks at the time metadata of the existing keys and
incorporates it into its DNSSEC policy operation. [GL #1706]
UDP network ports used for listening can no longer simultaneously be
used for sending traffic. An example configuration which triggers
this issue would be one which uses the same address:port pair for
listen-on(-v6) statements as for notify-source(-v6) or
transfer-source(-v6). While this issue affects all operating
systems, it only triggers log messages (e.g. “unable to create
dispatch for reserved port”) on some of them. There are currently no
plans to make such a combination of settings work again.
See above for a list of all known
issues affecting this BIND 9 branch.
The system-provided POSIX Threads read-write lock implementation is
now used by default instead of the native BIND 9 implementation.
Please be aware that glibc versions 2.26 through 2.29 had a
bug that
could cause BIND 9 to deadlock. A fix was released in glibc 2.30, and
most current Linux distributions have patched or updated glibc, with
the notable exception of Ubuntu 18.04 (Bionic) which is a work in
progress. If you are running on an affected operating system, compile
BIND 9 with --disable-pthread-rwlock until a fixed version of
glibc is available. [GL !3125]
A new asynchronous network communications system based on libuv
is now used by named for listening for incoming requests and
responding to them. This change will make it easier to improve
performance and implement new protocol layers (for example, DNS over
TLS) in the future. [GL #29]
The new dnssec-policy option allows the configuration of a key
and signing policy (KASP) for zones. This option enables named to
generate new keys as needed and automatically roll both ZSK and KSK
keys. (Note that the syntax for this statement differs from the
DNSSEC policy used by dnssec-keymgr.) [GL #1134]
In order to clarify the configuration of DNSSEC keys, the
trusted-keys and managed-keys statements have been
deprecated, and the new trust-anchors statement should now be
used for both types of key.
When used with the keyword initial-key, trust-anchors has the
same behavior as managed-keys, i.e., it configures a trust anchor
that is to be maintained via RFC 5011.
When used with the new keyword static-key, trust-anchors has
the same behavior as trusted-keys, i.e., it configures a
permanent trust anchor that will not automatically be updated. (This
usage is not recommended for the root key.) [GL #6]
Two new keywords have been added to the trust-anchors statement:
initial-ds and static-ds. These allow the use of trust
anchors in DS format instead of DNSKEY format. DS format allows trust
anchors to be configured for keys that have not yet been published;
this is the format used by IANA when announcing future root keys.
As with the initial-key and static-key keywords,
initial-ds configures a dynamic trust anchor to be maintained via
RFC 5011, and static-ds configures a permanent trust anchor.
[GL #6][GL #622]
dig, mdig and delv can all now take a +yaml option to
print output in a detailed YAML format. [GL #1145]
dig now has a new command line option: +[no]unexpected. By
default, dig won’t accept a reply from a source other than the
one to which it sent the query. Add the +unexpected argument to
enable it to process replies from unexpected sources. [RT #44978]
dig now accepts a new command line option, +[no]expandaaaa,
which causes the IPv6 addresses in AAAA records to be printed in full
128-bit notation rather than the default RFC 5952 format.
[GL #765]
Statistics channel groups can now be toggled. [GL #1030]
When static and managed DNSSEC keys were both configured for the same
name, or when a static key was used to configure a trust anchor for
the root zone and dnssec-validation was set to the default value
of auto, automatic RFC 5011 key rollovers would be disabled.
This combination of settings was never intended to work, but there
was no check for it in the parser. This has been corrected, and it is
now a fatal configuration error. [GL #868]
DS and CDS records are now generated with SHA-256 digests only,
instead of both SHA-1 and SHA-256. This affects the default output of
dnssec-dsfromkey, the dsset files generated by
dnssec-signzone, the DS records added to a zone by
dnssec-signzone based on keyset files, the CDS records added
to a zone by named and dnssec-signzone based on “sync” timing
parameters in key files, and the checks performed by
dnssec-checkds. [GL #1015]
named will now log a warning if a static key is configured for
the root zone. [GL #6]
A SipHash 2-4 based DNS Cookie (RFC 7873) algorithm has been added
and made default. Old non-default HMAC-SHA based DNS Cookie
algorithms have been removed, and only the default AES algorithm is
being kept for legacy reasons. This change has no operational impact
in most common scenarios. [GL #605]
If you are running multiple DNS servers (different versions of BIND 9
or DNS servers from multiple vendors) responding from the same IP
address (anycast or load-balancing scenarios), make sure that all the
servers are configured with the same DNS Cookie algorithm and same
Server Secret for the best performance.
The information from the dnssec-signzone and dnssec-verify
commands is now printed to standard output. The standard error output
is only used to print warnings and errors, and in case the user
requests the signed zone to be printed to standard output with the
-f- option. A new configuration option -q has been added to
silence all output on standard output except for the name of the
signed zone. [GL #1151]
The DNSSEC validation code has been refactored for clarity and to
reduce code duplication. [GL #622]
Compile-time settings enabled by the --with-tuning=large option
for configure are now in effect by default. Previously used
default compile-time settings can be enabled by passing
--with-tuning=small to configure. [GL !2989]
JSON-C is now the only supported library for enabling JSON support
for BIND statistics. The configure option has been renamed from
--with-libjson to --with-json-c. Set the PKG_CONFIG_PATH
environment variable accordingly to specify a custom path to the
json-c library, as the new configure option does not take the
library installation path as an optional argument. [GL #855]
./configure no longer sets --sysconfdir to /etc or
--localstatedir to /var when --prefix is not specified
and the aforementioned options are not specified explicitly. Instead,
Autoconf’s defaults of $prefix/etc and $prefix/var are
respected. [GL #658]
The dnssec-enable option has been obsoleted and no longer has any
effect. DNSSEC responses are always enabled if signatures and other
DNSSEC data are present. [GL #866]
DNSSEC Lookaside Validation (DLV) is now obsolete. The
dnssec-lookaside option has been marked as deprecated; when used
in named.conf, it will generate a warning but will otherwise be
ignored. All code enabling the use of lookaside validation has been
removed from the validator, delv, and the DNSSEC tools. [GL #7]
The cleaning-interval option has been removed. [GL !1731]
BIND 9.16 (Extended Support Version) will be supported until at least
December, 2023. See https://kb.isc.org/docs/aa-00896 for details of
ISC’s software support policy.
This document provides introductory information on how DNSSEC works, how
to configure BIND 9 to support some common DNSSEC features, and
some basic troubleshooting tips. The chapters are organized as follows:
Introduction covers the intended audience for this
document, assumed background knowledge, and a basic introduction to the
topic of DNSSEC.
Getting Started covers various requirements
before implementing DNSSEC, such as software versions, hardware
capacity, network requirements, and security changes.
Validation walks through setting up a validating
resolver, and gives both more information on the validation process and
some examples of tools to verify that the resolver is properly validating
answers.
Signing explains how to set up a basic signed
authoritative zone, details the relationship between a child and a parent zone,
and discusses ongoing maintenance tasks.
Thanks to the following individuals (in no particular order) who have
helped in completing this document: Jeremy C. Reed, Heidi Schempf,
Stephen Morris, Jeff Osborn, Vicky Risk, Jim Martin, Evan Hunt, Mark
Andrews, Michael McNally, Kelli Blucher, Chuck Aurora, Francis Dupont,
Rob Nagy, Ray Bellis, Matthijs Mekking, and Suzanne Goldlust.
Special thanks goes to Cricket Liu and Matt Larson for their
selflessness in knowledge sharing.
Thanks to all the reviewers and contributors, including John Allen, Jim
Young, Tony Finch, Timothe Litt, and Dr. Jeffry A. Spain.
The sections on key rollover and key timing metadata borrowed heavily
from the Internet Engineering Task Force draft titled “DNSSEC Key Timing
Considerations” by S. Morris, J. Ihren, J. Dickinson, and W. Mekking,
subsequently published as RFC 7583.
This guide is intended as an introduction to DNSSEC for the DNS
administrator who is already comfortable working with the existing BIND and DNS
infrastructure. He or she might be curious about DNSSEC, but may not have had the
time to investigate DNSSEC, to learn whether DNSSEC should
be a part of his or her environment, and understand what it means to deploy it in the
field.
This guide provides basic information on how to configure DNSSEC using
BIND 9.16.9 or later. Most of the information and examples in this guide also
apply to versions of BIND later than 9.9.0, but some of the key features described here
were only introduced in version 9.16.9. Readers are assumed to have basic
working knowledge of the Domain Name System (DNS) and related network
infrastructure, such as concepts of TCP/IP. In-depth knowledge of DNS and
TCP/IP is not required. The guide assumes no prior knowledge of DNSSEC or
related technology such as public key cryptography.
If you are already operating a DNSSEC-signed zone, you may not learn
much from the first half of this document, and you may want to start with
Advanced Discussions. If you want to
learn about details of the protocol extension, such as data fields and flags,
or the new record types, this document can help you get started but it
does not include all the technical details.
If you are experienced in DNSSEC, you
may find some of the concepts in this document to be overly simplified for
your taste, and some details are intentionally omitted at times for ease of
illustration.
If you administer a large or complex BIND environment, this
guide may not provide enough information for you, as it is intended to provide
only basic, generic working examples.
If you are a top-level domain (TLD) operator, or
administer zones under signed TLDs, this guide can
help you get started, but it does not provide enough details to serve all of your
needs.
If your DNS environment uses DNS products other than (or in addition to)
BIND, this document may provide some background or overlapping information, but you
should check each product’s vendor documentation for specifics.
Finally, deploying
DNSSEC on internal or private networks is not covered in this document, with the
exception of a brief discussion in DNSSEC on Private Networks.
The Domain Name System (DNS) was designed in a day and age when the
Internet was a friendly and trusting place. The protocol itself provides
little protection against malicious or forged answers. DNS Security
Extensions (DNSSEC) addresses this need, by adding digital signatures
into DNS data so that each DNS response can be verified for integrity
(the answer did not change during transit) and authenticity (the data
came from the true source, not an impostor). In the ideal world, when
DNSSEC is fully deployed, every single DNS answer can be validated and
trusted.
DNSSEC does not provide a secure tunnel; it does not encrypt or hide DNS
data. It operates independently of an existing Public Key Infrastructure
(PKI). It does not need SSL certificates or shared secrets. It was
designed with backwards compatibility in mind, and can be deployed
without impacting “old” unsecured domain names.
DNSSEC is deployed on the three major components of the DNS
infrastructure:
Recursive Servers: People use recursive servers to lookup external
domain names such as www.example.com. Operators of recursive servers
need to enable DNSSEC validation. With validation enabled, recursive
servers carry out additional tasks on each DNS response they
receive to ensure its authenticity.
Authoritative Servers: People who publish DNS data on their name
servers need to sign that data. This entails creating additional
resource records, and publishing them to parent domains where
necessary. With DNSSEC enabled, authoritative servers respond to
queries with additional DNS data, such as digital signatures and
keys, in addition to the standard answers.
Applications: This component lives on every client machine, from web
servers to smart phones. This includes resolver libraries on different
operating systems, and applications such as web browsers.
In this guide, we focus on the first two components, Recursive
Servers and Authoritative Servers, and only lightly touch on the third
component. We look at how DNSSEC works, how to configure a
validating resolver, how to sign DNS zone data, and other operational
tasks and considerations.
Public Key Cryptography works on the concept of a pair of keys: one
made available to the world publicly, and one kept in secrecy
privately. Not surprisingly, they are known as a public key and a private
key. If you are not familiar with the concept, think of it as a
cleverly designed lock, where one key locks and one key unlocks. In
DNSSEC, we give out the unlocking public key to the rest of the
world, while keeping the locking key private. To learn how this is
used to secure DNS messages, see How Are Answers Verified?.
DNSSEC introduces eight new resource record types:
RRSIG (digital resource record signature)
DNSKEY (public key)
DS (parent-child)
NSEC (proof of nonexistence)
NSEC3 (proof of nonexistence)
NSEC3PARAM (proof of nonexistence)
CDS (child-parent signaling)
CDNSKEY (child-parent signaling)
This guide does not go deep into the anatomy of each resource record
type; the details are left for the reader to research and explore.
Below is a short introduction on each of the new record types:
RRSIG: With DNSSEC enabled, just about every DNS answer (A, PTR,
MX, SOA, DNSKEY, etc.) comes with at least one resource
record signature, or RRSIG. These signatures are used by recursive name
servers, also known as validating resolvers, to verify the answers
received. To learn how digital signatures are generated and used, see
How Are Answers Verified?.
DNSKEY: DNSSEC relies on public-key cryptography for data
authenticity and integrity. There are several keys used in DNSSEC,
some private, some public. The public keys are published to the world
as part of the zone data, and they are stored in the DNSKEY record
type.
In general, keys in DNSSEC are used for one or both of the following
roles: as a Zone Signing Key (ZSK), used to protect all zone data; or
as a Key Signing Key (KSK), used to protect the zone’s keys. A key
that is used for both roles is referred to as a Combined Signing Key
(CSK). We talk about keys in more detail in
DNSSEC Keys.
DS: One of the critical components of DNSSEC is that the parent
zone can “vouch” for its child zone. The DS record is verifiable
information (generated from one of the child’s public keys) that a
parent zone publishes about its child as part of the chain of trust.
To learn more about the Chain of Trust, see
Chain of Trust.
NSEC, NSEC3, NSEC3PARAM: These resource records all deal with a
very interesting problem: proving that something does not exist. We
look at these record types in more detail in
Proof of Non-Existence (NSEC and NSEC3).
CDS, CDNSKEY: The CDS and CDNSKEY resource records apply to
operational matters and are a way to signal to the parent zone that
the DS records it holds for the child zone should be updated. This is
covered in more detail in The CDS and CDNSKEY Resource Records.
Traditional (insecure) DNS lookup is simple: a recursive name server
receives a query from a client to lookup a name like www.isc.org. The
recursive name server tracks down the authoritative name server(s)
responsible, sends the query to one of the authoritative name servers,
and waits for it to respond with the answer.
With DNSSEC validation enabled, a validating recursive name server
(a.k.a. a validating resolver) asks for additional resource
records in its query, hoping the remote authoritative name servers
respond with more than just the answer to the query, but some proof to
go along with the answer as well. If DNSSEC responses are received, the
validating resolver performs cryptographic computation to verify the
authenticity (the origin of the data) and integrity (that the data was not altered
during transit) of the answers, and even asks the parent zone as part of
the verification. It repeats this process of get-key, validate,
ask-parent, and its parent, and its parent, all the way until
the validating resolver reaches a key that it trusts. In the ideal,
fully deployed world of DNSSEC, all validating resolvers only need to
trust one key: the root key.
The 12-Step DNSSEC Validation Process (Simplified)
The following example shows the 12 steps of the DNSSEC validating process
at a very high level, looking up the name www.isc.org :
Upon receiving a DNS query from a client to resolve www.isc.org,
the validating resolver follows standard DNS protocol to track down
the name server for isc.org, and sends it a DNS query to ask for the
A record of www.isc.org. But since this is a DNSSEC-enabled
resolver, the outgoing query has a bit set indicating it wants
DNSSEC answers, hoping the name server that receives it is DNSSEC-enabled
and can honor this secure request.
The isc.org name server is DNSSEC-enabled, so it responds with both
the answer (in this case, an A record) and a digital signature for
verification purposes.
The validating resolver requires cryptographic keys to be able to verify the
digital signature, so it asks the isc.org name server for those keys.
The isc.org name server responds with the cryptographic keys
(and digital signatures of the keys) used to generate the digital
signature that was sent in #2. At this point, the validating
resolver can use this information to verify the answers received in
#2.
Let’s take a quick break here and look at what we’ve got so far…
how can our server trust this answer? If a clever attacker had taken over
the isc.org name server(s), of course she would send matching
keys and signatures. We need to ask someone else to have confidence
that we are really talking to the real isc.org name server. This
is a critical part of DNSSEC: at some point, the DNS administrators
at isc.org uploaded some cryptographic information to its
parent, .org, maybe through a secure web form, maybe
through an email exchange, or perhaps in person. In
any event, at some point some verifiable information about the
child (isc.org) was sent to the parent (.org) for
safekeeping.
The validating resolver asks the parent (.org) for the
verifiable information it keeps on its child, isc.org.
Verifiable information is sent from the .org server. At this
point, the validating resolver compares this to the answer it received
in #4; if the two of them match, it proves the authenticity of
isc.org.
Let’s examine this process. You might be thinking to yourself,
what if the clever attacker that took over isc.org also
compromised the .org servers? Of course all this information
would match! That’s why we turn our attention now to the
.org server, interrogate it for its cryptographic keys, and
move one level up to .org’s parent, root.
The validating resolver asks the .org authoritative name server for
its cryptographic keys, to verify the answers received in #6.
The .org name server responds with the answer (in this case,
keys and signatures). At this point, the validating resolver can
verify the answers received in #6.
The validating resolver asks root (.org’s parent) for the verifiable
information it keeps on its child, .org.
The root name server sends back the verifiable information it keeps
on .org. The validating resolver uses this information
to verify the answers received in #8.
So at this point, both isc.org and .org check out. But
what about root? What if this attacker is really clever and somehow
tricked us into thinking she’s the root name server? Of course she
would send us all matching information! So we repeat the
interrogation process and ask for the keys from the root name
server.
The validating resolver asks the root name server for its cryptographic
keys to verify the answer(s) received in #10.
The root name server sends its keys; at this point, the validating
resolver can verify the answer(s) received in #10.
But what about the root server itself? Who do we go to verify root’s
keys? There’s no parent zone for root. In security, you have to trust
someone, and in the perfectly protected world of DNSSEC (we talk later
about the current imperfect state and ways to work around it),
each validating resolver would only have to trust one entity, that is,
the root name server. The validating resolver already has the root key
on file (we discuss later how we got the root key file). So
after the answer in #12 is received, the validating resolver compares it
to the key it already has on file. Providing one of the keys in the
answer matches the one on file, we can trust the answer from root. Thus
we can trust .org, and thus we can trust isc.org. This is known
as the “chain of trust” in DNSSEC.
You might be thinking to yourself: all this DNSSEC stuff sounds
wonderful, but why should I care? Below are some reasons why you may
want to consider deploying DNSSEC:
Being a good netizen: By enabling DNSSEC validation (as described in
Validation) on your DNS servers, you’re protecting
your users and yourself a little more by checking answers returned to
you; by signing your zones (as described in
Signing), you are making it possible for other
people to verify your zone data. As more people adopt DNSSEC, the
Internet as a whole becomes more secure for everyone.
Compliance: You may not even get a say in
implementing DNSSEC, if your organization is subject to compliance
standards that mandate it. For example, the US government set a
deadline in 2008 to have all .gov subdomains signed by
December 2009 1. So if you operate a subdomain in .gov, you
must implement DNSSEC to be compliant. ICANN also requires
that all new top-level domains support DNSSEC.
Enhanced Security: Okay, so the big lofty goal of “let’s be good”
doesn’t appeal to you, and you don’t have any compliance standards to
worry about. Here is a more practical reason why you should consider
DNSSEC: in the event of a DNS-based security breach, such as cache
poisoning or domain hijacking, after all the financial and brand
damage done to your domain name, you might be placed under scrutiny
for any preventive measure that could have been put in place. Think
of this like having your website only available via HTTP but not
HTTPS.
New Features: DNSSEC brings not only enhanced security, but also
a whole new suite of features. Once DNS
can be trusted completely, it becomes possible to publish SSL
certificates in DNS, or PGP keys for fully automatic cross-platform
email encryption, or SSH fingerprints…. New features are still
being developed, but they all rely on a trustworthy DNS
infrastructure. To take a peek at these next-generation DNS features,
check out Introduction to DANE.
The Office of Management and Budget (OMB) for the US government
published a memo in
2008,
requesting all .gov subdomains to be DNSSEC-signed by December
2009. This explains why .gov is the most-deployed DNSSEC domain
currently, with around 90% of subdomains
signed.
How Does DNSSEC Change My Job as a DNS Administrator?
With this protocol extension, some of the things you were used to in DNS
have changed. As the DNS administrator, you have new maintenance
tasks to perform on a regular basis (as described in
Maintenance Tasks); when there is a DNS resolution
problem, you have new troubleshooting techniques and tools to use (as
described in Basic DNSSEC Troubleshooting). BIND 9 tries its best to
make these things as transparent and seamless as possible. In this
guide, we try to use configuration examples that result in the least
amount of work for BIND 9 DNS administrators.
Enabling DNSSEC validation on a recursive server makes it a validating
resolver. The job of a validating resolver is to fetch additional
information that can be used to computationally verify the answer set.
Contrary to popular belief, the increase in resource consumption is very modest:
CPU: a validating resolver executes cryptographic functions on cache-miss
answers, which leads to increased CPU usage. Thanks to standard DNS caching
and contemporary CPUs, the increase in CPU-time consumption in a steady
state is negligible - typically on the order of 5%. For a brief period (a few
minutes) after the resolver starts, the increase might be as much as 20%, but it
quickly decreases as the DNS cache fills in.
System memory: DNSSEC leads to larger answer sets and occupies
more memory space. With typical ISP traffic and the state of the Internet as
of mid-2022, memory consumption for the cache increases by roughly 20%.
Network interfaces: although DNSSEC does increase the amount of DNS
traffic overall, in practice this increase is often within measurement
error.
On the authoritative server side, DNSSEC is enabled on a zone-by-zone
basis. When a zone is DNSSEC-enabled, it is also known as “signed.”
Below are the expected changes to resource consumption caused by serving
DNSSEC-signed zones:
CPU: a DNSSEC-signed zone requires periodic re-signing, which is a
cryptographic function that is CPU-intensive. If your DNS zone is
dynamic or changes frequently, that also adds to higher CPU loads.
System storage: A signed zone is definitely larger than an unsigned
zone. How much larger? See
Your Zone, Before and After DNSSEC for a comparison
example. The final size depends on the structure of the zone, the signing algorithm,
the number of keys, the choice of NSEC or NSEC3, the ratio of signed delegations, the zone file
format, etc. Usually, the size of a signed zone ranges from a negligible
increase to as much as three times the size of the unsigned zone.
System memory: Larger DNS zone files take up not only more storage
space on the file system, but also more space when they are loaded
into system memory. The final memory consumption also depends on all the
variables listed above: in the typical case the increase is around half of
the unsigned zone memory consumption, but it can be as high as three times
for some corner cases.
Network interfaces: While your authoritative name servers will
begin sending back larger responses, it is unlikely that you need to
upgrade your network interface card (NIC) on the name server unless
you have some truly outdated hardware.
One factor to consider, but over which you really have no control, is
the number of users who query your domain name who themselves have DNSSEC
enabled. As of mid-2022, measurements by APNIC show 41% of Internet users send
DNSSEC-aware queries. This means that more DNS queries for your domain will
take advantage of the additional security features, which will result in
increased system load and possibly network traffic.
From a network perspective, DNS and DNSSEC packets are very similar;
DNSSEC packets are just bigger, which means DNS is more likely to use
TCP. You should test for the following two items to make sure your
network is ready for DNSSEC:
DNS over TCP: Verify network connectivity over TCP port 53, which
may mean updating firewall policies or Access Control Lists (ACL) on
routers. See Wait… DNS Uses TCP? for more details.
Large UDP packets: Some network equipment, such as firewalls, may
make assumptions about the size of DNS UDP packets and incorrectly
reject DNS traffic that appears “too big.” Verify that the
responses your name server generates are being seen by the rest of the
world: see What’s EDNS All About (And Why Should I Care)? for more details.
Before starting your DNSSEC deployment, check with your parent zone
administrators to make sure they support DNSSEC. This may or may not be
the same entity as your registrar. As you will see later in
Working With the Parent Zone, a crucial step in DNSSEC deployment
is establishing the parent-child trust relationship. If your parent zone
does not yet support DNSSEC, contact that administrator to voice your concerns.
Some organizations may be subject to stricter security requirements than
others. Check to see if your organization requires stronger
cryptographic keys be generated and stored, and how often keys need to be
rotated. The examples presented in this document are not intended for
high-value zones. We cover some of these security considerations in
Advanced Discussions.
This section provides the basic information needed to set up a
working DNSSEC-aware recursive server, also known as a validating
resolver. A validating resolver performs validation for each remote
response received, following the chain of trust to verify that the answers it
receives are legitimate, through the use of public key cryptography and
hashing functions.
So how do we turn on DNSSEC validation? It turns out that you may not need
to reconfigure your name server at all, since the most recent versions of BIND 9 -
including packages and distributions - have shipped with DNSSEC validation
enabled by default. Before making any configuration changes, check
whether you already have DNSSEC validation enabled by following the steps
described in So You Think You Are Validating (How To Test A Recursive Server).
In earlier versions of BIND, including 9.11-ESV, DNSSEC
validation must be explicitly enabled. To do this, you only need to
add one line to the options section of your configuration file:
options{...dnssec-validationauto;...};
Restart named or run rndcreconfig, and your recursive server is
now happily validating each DNS response. If this does not work for you,
you may have some other network-related configurations that need to be
adjusted. Take a look at Network Requirements to make sure your network
is ready for DNSSEC.
Once DNSSEC validation is enabled, any DNS response that does not pass
the validation checks results in a failure to resolve the domain name
(often a SERVFAIL status seen by the client). If everything has
been configured properly, this is the correct result; it means that an end user has
been protected against a malicious attack.
However, if there is a DNSSEC configuration issue (sometimes outside of
the administrator’s control), a specific name or sometimes entire
domains may “disappear” from the DNS, and become unreachable
through that resolver. For the end user, the issue may manifest itself
as name resolution being slow or failing altogether; some parts of a URL
not loading; or the web browser returning an error message indicating
that the page cannot be displayed. For example, if root name
servers were misconfigured with the wrong information about .org, it
could cause all validation for .org domains to fail. To end
users, it would appear that all .org web
sites were out of service 2. Should you encounter DNSSEC-related problems, don’t be
tempted to disable validation; there is almost certainly a solution that
leaves validation enabled. A basic troubleshooting guide can be found in
Basic DNSSEC Troubleshooting.
Of course, something like this could happen for reasons other than
DNSSEC: for example, the root publishing the wrong addresses for the
.org nameservers.
So You Think You Are Validating (How To Test A Recursive Server)
Now that you have reconfigured your recursive server and
restarted it, how do you know that your recursive name server is
actually verifying each DNS query? There are several ways to check, and
we’ve listed a few of them below.
For most people, the simplest way to check if a recursive name server
is indeed validating DNS queries is to use one of the many web-based
tools available.
Configure your client computer to use the newly reconfigured recursive
server for DNS resolution; then use one of these web-based tests to
confirm that it is in fact validating DNS responses.
Web-based DNSSEC-verification tools often employ JavaScript. If you don’t trust the
JavaScript magic that the web-based tools rely on, you can take matters
into your own hands and use a command-line DNS tool to check your
validating resolver yourself.
While nslookup is popular, partly because it comes pre-installed on
most systems, it is not DNSSEC-aware. dig, on the other hand, fully
supports the DNSSEC standard and comes as a part of BIND. If you do not
have dig already installed on your system, install it by downloading
it from ISC’s website. ISC provides pre-compiled
Windows versions on its website.
dig is a flexible tool for interrogating DNS name servers. It
performs DNS lookups and displays the answers that are returned from the
name servers that were queried. Most seasoned DNS administrators use
dig to troubleshoot DNS problems because of its flexibility, ease of
use, and clarity of output.
The example below shows how to use dig to query the name server 10.53.0.1
for the A record for ftp.isc.org when DNSSEC validation is enabled
(i.e. the default). The address 10.53.0.1 is only used as an example;
replace it with the actual address or host name of your
recursive name server.
$ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline
; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good)
;; QUESTION SECTION:
;ftp.isc.org. IN A
;; ANSWER SECTION:
ftp.isc.org. 300 IN A 149.20.1.49
ftp.isc.org. 300 IN RRSIG A 13 3 300 (
20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== )
;; Query time: 452 msec
;; SERVER: 10.53.0.1#53(10.53.0.1)
;; WHEN: Tue Mar 10 14:30:57 GMT 2020
;; MSG SIZE rcvd: 187
The important detail in this output is the presence of the ad flag
in the header. This signifies that BIND has retrieved all related DNSSEC
information related to the target of the query (ftp.isc.org) and that
the answer received has passed the validation process described in
How Are Answers Verified?. We can have confidence in the
authenticity and integrity of the answer, that ftp.isc.org really
points to the IP address 149.20.1.49, and that it was not a spoofed answer
from a clever attacker.
Unlike earlier versions of BIND, the current versions of BIND always
request DNSSEC records (by setting the do bit in the query they make
to upstream servers), regardless of DNSSEC settings. However, with
validation disabled, the returned signature is not checked. This can be
seen by explicitly disabling DNSSEC validation. To do this, add the line
dnssec-validationno; to the “options” section of the configuration
file, i.e.:
options{...dnssec-validationno;...};
If the server is restarted (to ensure a clean cache) and the same
dig command executed, the result is very similar:
$ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline
; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39050
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: a8dc9d1b9ec45e75010000005e67a8a69399741fdbe126f2 (good)
;; QUESTION SECTION:
;ftp.isc.org. IN A
;; ANSWER SECTION:
ftp.isc.org. 300 IN A 149.20.1.49
ftp.isc.org. 300 IN RRSIG A 13 3 300 (
20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== )
;; Query time: 261 msec
;; SERVER: 10.53.0.1#53(10.53.0.1)
;; WHEN: Tue Mar 10 14:48:06 GMT 2020
;; MSG SIZE rcvd: 187
However, this time there is no ad flag in the header. Although
dig is still returning the DNSSEC-related resource records, it is
not checking them, and thus cannot vouch for the authenticity of the answer.
If you do carry out this test, remember to re-enable DNSSEC validation
(by removing the dnssec-validationno; line from the configuration
file) before continuing.
It is also important to make sure that DNSSEC is protecting your network from
domain names that fail to validate; such failures could be caused by
attacks on your system, attempting to get it to accept false DNS
information. Validation could fail for a number of reasons: maybe the
answer doesn’t verify because it’s a spoofed response; maybe the
signature was a replayed network attack that has expired; or maybe the
child zone has been compromised along with its keys, and the parent
zone’s information tells us that things don’t add up. There is a
domain name specifically set up to fail DNSSEC validation,
www.dnssec-failed.org.
With DNSSEC validation enabled (the default), an attempt to look up that
name fails:
On the other hand, if DNSSEC validation is disabled (by adding the
statement dnssec-validationno; to the options clause in the
configuration file), the lookup succeeds:
$ dig @10.53.0.1 www.dnssec-failed.org. A
; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54704
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 251eee58208917f9010000005e67bb6829f6dabc5ae6b7b9 (good)
;; QUESTION SECTION:
;www.dnssec-failed.org. IN A
;; ANSWER SECTION:
www.dnssec-failed.org. 7200 IN A 68.87.109.242
www.dnssec-failed.org. 7200 IN A 69.252.193.191
;; Query time: 439 msec
;; SERVER: 10.53.0.1#53(10.53.0.1)
;; WHEN: Tue Mar 10 16:08:08 GMT 2020
;; MSG SIZE rcvd: 110
Do not be tempted to disable DNSSEC validation just because some names
are failing to resolve. Remember, DNSSEC protects your DNS lookup from
hacking. The next section describes how to quickly check whether
the failure to successfully look up a name is due to a validation
failure.
Since all DNSSEC validation failures result in a general SERVFAIL
message, how do we know if it was really a validation error?
Fortunately, there is a flag in dig, (+cd, for “checking
disabled”) which tells the server to disable DNSSEC validation. If
you receive a SERVFAIL message, re-run the query a second time
and set the +cd flag. If the query succeeds with +cd, but
ends in SERVFAIL without it, you know you are dealing with a
validation problem. So using the previous example of
www.dnssec-failed.org and with DNSSEC validation enabled in the
resolver:
$ dig @10.53.0.1 www.dnssec-failed.org A +cd
; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A +cd
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62313
;; flags: qr rd ra cd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 73ca1be3a74dd2cf010000005e67c8c8e6df64b519cd87fd (good)
;; QUESTION SECTION:
;www.dnssec-failed.org. IN A
;; ANSWER SECTION:
www.dnssec-failed.org. 7197 IN A 68.87.109.242
www.dnssec-failed.org. 7197 IN A 69.252.193.191
;; Query time: 0 msec
;; SERVER: 10.53.0.1#53(10.53.0.1)
;; WHEN: Tue Mar 10 17:05:12 GMT 2020
;; MSG SIZE rcvd: 110
In Easy-Start Guide for Recursive Servers, we used one line
of configuration to turn on DNSSEC validation: the act of chasing down
signatures and keys, making sure they are authentic. Now we are going to
take a closer look at what DNSSEC validation actually does, and some other options.
This “auto” line enables automatic DNSSEC trust anchor configuration
using the managed-keys feature. In this case, no manual key
configuration is needed. There are three possible choices for the
dnssec-validation option:
yes: DNSSEC validation is enabled, but a trust anchor must be
manually configured. No validation actually takes place until
at least one trusted key has been manually configured.
no: DNSSEC validation is disabled, and the recursive server behaves
in the “old-fashioned” way of performing insecure DNS lookups.
auto: DNSSEC validation is enabled, and a default trust anchor
(included as part of BIND 9) for the DNS root zone is used. This is the
default; BIND automatically does this if there is no
dnssec-validation line in the configuration file.
Let’s discuss the difference between yes and auto. If set to
yes, the trust anchor must be manually defined and maintained
using the trust-anchors statement (with either the static-key or
static-ds modifier) in the configuration file; if set to
auto (the default, and as shown in the example), then no further
action should be required as BIND includes a copy 3 of the root key.
When set to auto, BIND automatically keeps the keys (also known as
trust anchors, discussed in Trust Anchors)
up-to-date without intervention from the DNS administrator.
We recommend using the default auto unless there is a good reason to
require a manual trust anchor. To learn more about trust anchors,
please refer to Trusted Keys and Managed Keys.
Now you’ve enabled validation on your recursive name server and
verified that it works. What exactly changed? In
How Does DNSSEC Change DNS Lookup? we looked at a very
high-level, simplified version of the 12 steps of the DNSSEC validation process. Let’s revisit
that process now and see what your validating resolver is doing in more
detail. Again, as an example we are looking up the A record for the
domain name www.isc.org (see The 12-Step DNSSEC Validation Process (Simplified)):
The validating resolver queries the isc.org name servers for the
A record of www.isc.org. This query has the DNSSECOK (do) bit set to 1, notifying the remote authoritative
server that DNSSEC answers are desired.
Since the zone isc.org is signed, and its name servers are
DNSSEC-aware, it responds with the answer to the A record query plus
the RRSIG for the A record.
The validating resolver queries for the DNSKEY for isc.org.
The isc.org name server responds with the DNSKEY and RRSIG
records. The DNSKEY is used to verify the answers received in #2.
The validating resolver queries the parent (.org) for the DS
record for isc.org.
The .org name server is also DNSSEC-aware, so it responds with the
DS and RRSIG records. The DS record is used to verify the answers
received in #4.
The validating resolver queries for the DNSKEY for .org.
The .org name server responds with its DNSKEY and RRSIG. The DNSKEY
is used to verify the answers received in #6.
The validating resolver queries the parent (root) for the DS record
for .org.
The root name server, being DNSSEC-aware, responds with DS and RRSIG
records. The DS record is used to verify the answers received in #8.
The validating resolver queries for the DNSKEY for root.
The root name server responds with its DNSKEY and RRSIG. The DNSKEY is
used to verify the answers received in #10.
After step #12, the validating resolver takes the DNSKEY received and
compares it to the key or keys it has configured, to decide whether
the received key can be trusted. We talk about these locally
configured keys, or trust anchors, in Trust Anchors.
With DNSSEC, every response includes not just the
answer, but a digital signature (RRSIG) as well, so the
validating resolver can verify the answer received. That is what we
look at in the next section, How Are Answers Verified?.
Keep in mind, as you read this section, that although words like
“encryption” and “decryption”
are used here from time to time, DNSSEC does not provide privacy.
Public key cryptography is used to verify data authenticity (who
sent it) and data integrity (it did not change during transit), but
any eavesdropper can still see DNS requests and responses in
clear text, even when DNSSEC is enabled.
So how exactly are DNSSEC answers verified? Let’s first see how verifiable information is
generated. On the authoritative server, each DNS record (or message) is
run through a hash function, and this hashed value is then encrypted by a
private key. This encrypted hash value is the digital signature.
When the validating resolver queries for the resource record, it
receives both the plain-text message and the digital signature(s). The
validating resolver knows the hash function used (it is listed in the digital
signature record itself), so it can take the plain-text message and run
it through the same hash function to produce a hashed value, which we’ll call
hash value X. The validating resolver can also obtain the public key
(published as DNSKEY records), decrypt the digital signature, and get
back the original hashed value produced by the authoritative server,
which we’ll call hash value Y. If hash values X and Y are identical, and
the time is correct (more on what this means below), the answer is
verified, meaning this answer came from the authoritative server
(authenticity), and the content remained intact during transit
(integrity).
When a validating resolver queries for the A record ftp.isc.org, it
receives both the A record and the RRSIG record. It runs the A record
through a hash function (in this example, SHA256 as
indicated by the number 13, signifying ECDSAP256SHA256) and produces
hash value X. The resolver also fetches the appropriate DNSKEY record to
decrypt the signature, and the result of the decryption is hash value Y.
But wait, there’s more! Just because X equals Y doesn’t mean everything
is good. We still have to look at the time. Remember we mentioned a
little earlier that we need to check if the time is correct? Look
at the two timestamps in our example above:
Signature Expiration: 20200401191851
Signature Inception: 20200302184340
This tells us that this signature was generated UTC March 2nd, 2020, at
6:43:40 PM (20200302184340), and it is good until UTC April 1st, 2020,
7:18:51 PM (20200401191851). The validating resolver’s current
system time needs to fall between these two timestamps. If it does not, the
validation fails, because it could be an attacker replaying an old
captured answer set from the past, or feeding us a crafted one with
incorrect future timestamps.
If the answer passes both the hash value check and the timestamp check, it is
validated and the authenticated data (ad) bit is set, and the response
is sent to the client; if it does not verify, a SERVFAIL is returned to
the client.
BIND technically includes two copies of the root key: one is in
bind.keys.h and is built into the executable, and one is in
bind.keys as a trust-anchors statement. The two copies of the
key are identical.
A trust anchor is a key that is placed into a validating resolver, so
that the validator can verify the results of a given request with a
known or trusted public key (the trust anchor). A validating resolver
must have at least one trust anchor installed to perform DNSSEC
validation.
In the section How Does DNSSEC Change DNS Lookup (Revisited)?,
we walked through the 12 steps of the DNSSEC lookup process. At the end
of the 12 steps, a critical comparison happens: the key received from
the remote server and the key we have on file are compared to see if we
trust it. The key we have on file is called a trust anchor, sometimes
also known as a trust key, trust point, or secure entry point.
The 12-step lookup process describes the DNSSEC lookup in the ideal
world, where every single domain name is signed and properly delegated,
and where each validating resolver only needs to have one trust anchor - that
is, the root’s public key. But there is no restriction that the
validating resolver must only have one trust anchor. In fact, in the
early stages of DNSSEC adoption, it was not unusual for a validating
resolver to have more than one trust anchor.
For instance, before the root zone was signed (in July 2010), some
validating resolvers that wished to validate domain names in the .gov
zone needed to obtain and install the key for .gov. A sample lookup
process for www.fbi.gov at that time would have been eight steps rather
than 12:
The validating resolver queried fbi.gov name server for the A
record of www.fbi.gov.
The FBI’s name server responded with the answer and its RRSIG.
The validating resolver queried the FBI’s name server for its DNSKEY.
The FBI’s name server responded with the DNSKEY and its RRSIG.
The validating resolver queried a .gov name server for the DS
record of fbi.gov.
The .gov name server responded with the DS record and the
associated RRSIG for fbi.gov.
The validating resolver queried the .gov name server for its DNSKEY.
The .gov name server responded with its DNSKEY and the associated
RRSIG.
This all looks very similar, except it’s shorter than the 12 steps that
we saw earlier. Once the validating resolver receives the DNSKEY file in
#8, it recognizes that this is the manually configured trusted key
(trust anchor), and never goes to the root name servers to ask for the
DS record for .gov, or ask the root name servers for their DNSKEY.
In fact, whenever the validating resolver receives a DNSKEY, it checks
to see if this is a configured trusted key to decide whether it
needs to continue chasing down the validation chain.
Since the resolver is validating, we must have at least one key (trust
anchor) configured. How did it get here, and how do we maintain it?
If you followed the recommendation in
Easy-Start Guide for Recursive Servers, by setting
dnssec-validation to auto, there is nothing left to do.
BIND already includes a copy of the root key (in the file
bind.keys), and automatically updates it when the root key
changes. 4 It looks something like this:
trust-anchors{# This key (20326) was published in the root zone in 2017..initial-key25738"AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=";};
You can, of course, decide to manage this key manually yourself.
First, you need to make sure that dnssec-validation is set
to yes rather than auto:
options{dnssec-validationyes;};
Then, download the root key manually from a trustworthy source, such as
https://www.isc.org/bind-keys. Finally, take the root key you
manually downloaded and put it into a trust-anchors statement as
shown below:
trust-anchors{# This key (20326) was published in the root zone in 2017..static-key25738"AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=";};
While this trust-anchors statement and the one in the bind.keys
file appear similar, the definition of the key in bind.keys has the
initial-key modifier, whereas in the statement in the configuration
file, that is replaced by static-key. There is an important
difference between the two: a key defined with static-key is always
trusted until it is deleted from the configuration file. With the
initial-key modified, keys are only trusted once: for as long as it
takes to load the managed key database and start the key maintenance
process. Thereafter, BIND uses the managed keys database
(managed-keys.bind.jnl) as the source of key information.
Warning
Remember, if you choose to manage the keys on your own, whenever the
key changes (which, for most zones, happens on a periodic basis),
the configuration needs to be updated manually. Failure to do so will
result in breaking nearly all DNS queries for the subdomain of the
key. So if you are manually managing .gov, all domain names in
the .gov space may become unresolvable; if you are manually
managing the root key, you could break all DNS requests made to your
recursive name server.
Explicit management of keys was common in the early days of DNSSEC, when
neither the root zone nor many top-level domains were signed. Since
then, over 90% of
the top-level domains have been signed, including all the largest ones.
Unless you have a particular need to manage keys yourself, it is best to
use the BIND defaults and let the software manage the root key.
The root zone was signed in July 2010 and, as at the time of this writing
(mid-2020), the key has been changed once, in October 2018. The intention going
forward is to roll the key once every five years.
Traditional DNS responses are typically small in size (less than 512
bytes) and fit nicely into a small UDP packet. The Extension mechanism
for DNS (EDNS, or EDNS(0)) offers a mechanism to send DNS data in
larger packets over UDP. To support EDNS, both the DNS server
and the network need to be properly prepared to support the larger
packet sizes and multiple fragments.
This is important for DNSSEC, since the +do bit that signals
DNSSEC-awareness is carried within EDNS, and DNSSEC responses are larger
than traditional DNS ones. If DNS servers and the network environment cannot
support large UDP packets, it will cause retransmission over TCP, or the
larger UDP responses will be discarded. Users will likely experience
slow DNS resolution or be unable to resolve certain names at all.
Note that EDNS applies regardless of whether you are validating DNSSEC, because
BIND has DNSSEC enabled by default.
Please see Network Requirements for more information on what
DNSSEC expects from the network environment.
For many years, BIND has had EDNS enabled by default,
and the UDP packet size is set to a maximum of 4096 bytes. The DNS
administrator should not need to perform any reconfiguration. You can
use dig to verify that your server supports EDNS and see the UDP packet
size it allows with this dig command:
$ dig @10.53.0.1 www.isc.org. A +dnssec +multiline
; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good)
;; QUESTION SECTION:
;ftp.isc.org. IN A
;; ANSWER SECTION:
ftp.isc.org. 300 IN A 149.20.1.49
ftp.isc.org. 300 IN RRSIG A 13 3 300 (
20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== )
;; Query time: 452 msec
;; SERVER: 10.53.0.1#53(10.53.0.1)
;; WHEN: Tue Mar 10 14:30:57 GMT 2020
;; MSG SIZE rcvd: 187
Once you’ve verified that your name servers have EDNS enabled, that should be the
end of the story, right? Unfortunately, EDNS is a hop-by-hop extension
to DNS. This means the use of EDNS is negotiated between each pair of
hosts in a DNS resolution process, which in turn means if one of your
upstream name servers (for instance, your ISP’s recursive name server
that your name server forwards to) does not support EDNS, you may experience DNS
lookup failures or be unable to perform DNSSEC validation.
If both your recursive name server and your ISP’s name servers
support EDNS, we are all good here, right? Not so fast. Since these large
packets have to traverse the network, the network infrastructure
itself must allow them to pass.
When data is physically transmitted over a network, it has to be broken
down into chunks. The size of the data chunk is known as the Maximum
Transmission Unit (MTU), and it can differ from network to
network. IP fragmentation occurs when a large data packet needs to be
broken down into chunks smaller than the
MTU; these smaller chunks then need to be reassembled back into the large
data packet at their destination. IP fragmentation is not necessarily a bad thing, and it most
likely occurs on your network today.
Some network equipment, such as a firewall, may make assumptions about
DNS traffic. One of these assumptions may be how large each DNS packet
is. When a firewall sees a larger DNS packet than it expects, it may either
reject the large packet or drop its fragments because the firewall
thinks it’s an attack. This configuration probably didn’t cause problems
in the past, since traditional DNS packets are usually pretty small in
size. However, with DNSSEC, these configurations need to be updated,
since DNSSEC traffic regularly exceeds 1500 bytes (a common MTU value).
If the configuration is not updated to support a larger DNS packet size,
it often results in the larger packets being rejected, and to the
end user it looks like the queries go unanswered. Or in the case of
fragmentation, only a part of the answer makes it to the validating
resolver, and your validating resolver may need to re-ask the question
again and again, creating the appearance for end users that the DNS/network is slow.
While you are updating the configuration on your network equipment, make
sure TCP port 53 is also allowed for DNS traffic.
Yes. DNS uses TCP port 53 as a fallback mechanism, when it cannot use
UDP to transmit data. This has always been the case, even long before
the arrival of DNSSEC. Traditional DNS relies on TCP port 53 for
operations such as zone transfer. The use of DNSSEC, or DNS with IPv6
records such as AAAA, increases the chance that DNS data will be
transmitted via TCP.
Due to the increased packet size, DNSSEC may fall back to TCP more often
than traditional (insecure) DNS. If your network blocks or
filters TCP port 53 today, you may already experience instability with
DNS resolution, before even deploying DNSSEC.
This section provides the basic information needed to set up a
DNSSEC-enabled authoritative name server. A DNSSEC-enabled (or
“signed”) zone contains additional resource records that are used to
verify the authenticity of its zone information.
To convert a traditional (insecure) DNS zone to a secure one, we need to
create some additional records (DNSKEY, RRSIG, and NSEC or NSEC3), and
upload verifiable information (such as a DS record) to the parent zone to
complete the chain of trust. For more information about DNSSEC resource
records, please see What Does DNSSEC Add to DNS?.
Note
In this chapter, we assume all configuration files, key files, and
zone files are stored in /etc/bind, and most examples show
commands run as the root user. This may not be ideal, but the point is
not to distract from what is important here: learning how to sign
a zone. There are many best practices for deploying a more secure
BIND installation, with techniques such as jailed process and
restricted user privileges, but those are not covered
in this document. We trust you, a responsible DNS
administrator, to take the necessary precautions to secure your
system.
For the examples below, we work with the assumption that
there is an existing insecure zone example.com that we are
converting to a secure zone.
Enabling Automated DNSSEC Zone Maintenance and Key Generation
To sign a zone, add the following statement to its
zone clause in the BIND 9 configuration file:
The dnssec-policy statement causes the zone to be signed and turns
on automatic maintenance for the zone. This includes re-signing the zone
as signatures expire and replacing keys on a periodic basis. The value
default selects the default policy, which contains values suitable
for most situations. We cover the creation of a custom policy in
Creating a Custom DNSSEC Policy, but for the moment we are accepting the
default values.
Using dnssec-policy requires dynamic DNS or inline-signing
to be enabled.
Note
Previously, if a zone with a dnssec-policy did not have dynamic
DNS set up and inline-signing was not explicity set, BIND 9 used
inline-signing implicitly. But this caused a lot of problems when operators
switched on or off dynamic DNS for their zones. Therefor, you now have to
configure it explicitly.
When the configuration file is updated, tell named to
reload the configuration file by running rndcreconfig:
# rndc reconfig
And that’s it - BIND signs your zone.
At this point, before you go away and merrily add dnssec-policy
statements to all your zones, we should mention that, like a number of
other BIND configuration options, its scope depends on where it is placed. In
the example above, we placed it in a zone clause, so it applied only
to the zone in question. If we had placed it in a view clause, it
would have applied to all zones in the view; and if we had placed it in
the options clause, it would have applied to all zones served by
this instance of BIND.
The BIND 9 reconfiguration starts the process of signing the zone.
First, it generates a key for the zone and includes it
in the published zone. The log file shows messages such as these:
It then starts signing the zone. How long this process takes depends on the
size of the zone, the speed of the server, and how much activity is
taking place. We can check what is happening by using rndc,
entering the command:
# rndc signing -list example.com
While the signing is in progress, the output is something like:
Signingwithkey10376/ECDSAP256SHA256
and when it is finished:
Donesigningwithkey10376/ECDSAP256SHA256
When the second message appears, the zone is signed.
Before moving on to the next step of coordinating with the parent zone,
let’s make sure everything looks good using delv. We want to
simulate what a validating resolver will check, by telling
delv to use a specific trust anchor.
First, we need to make a copy of the key created by BIND. This
is in the directory you set with the directory statement in
your configuration file’s options clause, and is named something
like Kexample.com.+013.10376.key:
Now we can run the delv command and instruct it to use this
trusted-key file to validate the answer it receives from the
authoritative name server 192.168.1.13:
$ delv @192.168.1.13 -a /tmp/example.key +root=example.com example.com. SOA +multiline
; fully validated
example.com. 600 IN SOA ns1.example.com. admin.example.com. (
2020040703 ; serial
1800 ; refresh (30 minutes)
900 ; retry (15 minutes)
2419200 ; expire (4 weeks)
300 ; minimum (5 minutes)
)
example.com. 600 IN RRSIG SOA 13 2 600 (
20200421150255 20200407140255 10376 example.com.
jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF
oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== )
Once everything is complete on our name server, we need to generate some
information to be uploaded to the parent zone to complete the chain of
trust. The format and the upload methods are actually dictated by your
parent zone’s administrator, so contact your registrar or parent zone
administrator to find out what the actual format should be and how to
deliver or upload the information to the parent zone.
What about your zone between the time you signed it and the time your
parent zone accepts the upload? To the rest of the world, your
zone still appears to be insecure, because if a validating
resolver attempts to validate your domain name via
your parent zone, your parent zone will indicate that you are
not yet signed (as far as it knows). The validating resolver will then
give up attempting to validate your domain name, and will fall back to the
insecure DNS. Until you complete this final step with your
parent zone, your zone remains insecure.
Note
Before uploading to your parent zone, verify that your newly signed
zone has propagated to all of your name servers (usually via zone
transfers). If some of your name servers still have unsigned zone
data while the parent tells the world it should be signed, validating
resolvers around the world cannot resolve your domain name.
Here are some examples of what you may upload to your parent zone, with
the DNSKEY/DS data shortened for display. Note that no matter what
format may be required, the end result is the parent zone
publishing DS record(s) based on the information you upload. Again,
contact your parent zone administrator(s) to find out the
correct format for their system.
The DS record format may be generated from the DNSKEY using the
dnssec-dsfromkey tool, which is covered in
DS Record Format. For more details and examples on how
to work with your parent zone, please see
Working With the Parent Zone.
Congratulations! Your zone is signed, your secondary servers have
received the new zone data, and the parent zone has accepted your upload
and published your DS record. Your zone is now officially
DNSSEC-enabled. What happens next? That is basically it - BIND
takes care of everything else. As for updating your zone file, you can
continue to update it the same way as prior to signing your
zone; the normal work flow of editing a zone file and using the rndc
command to reload the zone still works as usual, and although you are
editing the unsigned version of the zone, BIND generates the signed
version automatically.
Curious as to what all these commands did to your zone file? Read on to
Your Zone, Before and After DNSSEC and find out. If you are
interested in how to roll this out to your existing primary and
secondary name servers, check out DNSSEC Signing in
the Recipes chapter.
When we assigned the default DNSSEC policy to the zone, we provided the
minimal amount of information to convert a traditional DNS
zone into a DNSSEC-enabled zone. This is what the zone looked like
before we started:
$ dig @192.168.1.13 example.com. AXFR +multiline +onesoa
; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com AXFR +multiline +onesoa
; (1 server found)
;; global options: +cmd
example.com. 600 IN SOA ns1.example.com. admin.example.com. (
2020040700 ; serial
1800 ; refresh (30 minutes)
900 ; retry (15 minutes)
2419200 ; expire (4 weeks)
300 ; minimum (5 minutes)
)
example.com. 600 IN NS ns1.example.com.
ftp.example.com. 600 IN A 192.168.1.200
ns1.example.com. 600 IN A 192.168.1.1
web.example.com. 600 IN CNAME www.example.com.
www.example.com. 600 IN A 192.168.1.100
Below shows the test zone example.com after reloading the
server configuration. Clearly, the zone grew in size, and the
number of records multiplied:
But this is a really messy way to tell if the zone is set up properly
with DNSSEC. Fortunately, there are tools to help us with that. Read on
to How To Test Authoritative Zones to learn more.
One way to see if your zone is signed is to check for the
presence of DNSKEY record types. In our example, we created a single
key, and we expect to see it returned when we query for it.
$ dig @192.168.1.13 example.com. DNSKEY +multiline
; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com DNSKEY +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18637
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: efe186423313fb66010000005e8c997e99864f7d69ed7c11 (good)
;; QUESTION SECTION:
;example.com. IN DNSKEY
;; ANSWER SECTION:
example.com. 3600 IN DNSKEY 257 3 13 (
6saiq99qDBb5b4G4cx13cPjFTrIvUs3NW44SvbbHorHb
kXwOzeGAWyPORN+pwEV/LP9+FHAF/JzAJYdqp+o0dw==
) ; KSK; alg = ECDSAP256SHA256 ; key id = 10376
Another way to see if your zone data is signed is to check for the
presence of a signature. With DNSSEC, every record 5 now comes with at
least one corresponding signature, known as an RRSIG.
$ dig @192.168.1.13 example.com. SOA +dnssec +multiline
; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com SOA +dnssec +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45219
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 75adff4f4ce916b2010000005e8c99c0de47eabb7951b2f5 (good)
;; QUESTION SECTION:
;example.com. IN SOA
;; ANSWER SECTION:
example.com. 600 IN SOA ns1.example.com. admin.example.com. (
2020040703 ; serial
1800 ; refresh (30 minutes)
900 ; retry (15 minutes)
2419200 ; expire (4 weeks)
300 ; minimum (5 minutes)
)
example.com. 600 IN RRSIG SOA 13 2 600 (
20200421150255 20200407140255 10376 example.com.
jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF
oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== )
The serial number was automatically incremented from the old, unsigned
version. named keeps track of the serial number of the signed version of
the zone independently of the unsigned version. If the unsigned zone is
updated with a new serial number that is higher than the one in the
signed copy, then the signed copy is increased to match it;
otherwise, the two are kept separate.
Our original zone file example.com.db remains untouched, and named has
generated three additional files automatically for us (shown below). The
signed DNS data is stored in example.com.db.signed and in the
associated journal file.
# cd /etc/bind# lsexample.com.dbexample.com.db.jbkexample.com.db.signedexample.com.db.signed.jnl
A quick description of each of the files:
.jbk: a transient file used by named
.signed: the signed version of the zone in raw format
.signed.jnl: a journal file for the signed version of the zone
These files are stored in raw (binary) format for faster loading. To
reveal the human-readable version, use named-compilezone
as shown below. In the example below, we run the command on the
raw format zone example.com.db.signed to produce a text version of
the zone example.com.text:
# named-compilezone -f raw -F text -o example.com.text example.com example.com.db.signedzoneexample.com/IN:loadedserial2014112008(DNSSECsigned)dumpzonetoexample.com.text...doneOK
Although this is not strictly related to whether the zone is
signed, a critical part of DNSSEC is the trust relationship between the
parent and the child. Just because we, the child, have all the correctly
signed records in our zone does not mean it can be fully validated by a
validating resolver, unless our parent’s data agrees with ours. To check
if our upload to the parent was successful, ask the parent name server
for the DS record of our child zone; we should get back the DS record(s)
containing the information we uploaded in
Uploading Information to the Parent Zone:
Well, almost every record: NS records and glue records for
delegations do not have RRSIG records. If there are
no delegations, then every record in your zone is
signed and comes with its own RRSIG.
We recommend two tools, below: Verisign DNSSEC Debugger and DNSViz. Others can
be found via a simple online search. These excellent online tools are an easy
way to verify that your domain name is fully secured.
This tool shows a nice summary of checks performed on your domain name.
You can expand it to view more details for each of the items checked, to
get a detailed report.
Signing a zone requires a number of separate steps:
Generation of the keys to sign the zone.
Inclusion of the keys into the zone.
Signing of the records in the file (including the generation of the
NSEC or NSEC3 records).
Maintaining a signed zone comprises a set of ongoing tasks:
Re-signing the zone as signatures approach expiration.
Generation of new keys as the time approaches for a key roll.
Inclusion of new keys into the zone when the rollover starts.
Transition from signing the zone with the old set of keys to signing
the zone with the new set of keys.
Waiting the appropriate interval before removing the old keys from
the zone.
Deleting the old keys.
That is quite complex, and it is all handled in BIND 9 with the single
dnssec-policydefault statement. We will see later on (in the
Creating a Custom DNSSEC Policy section) how these actions can be tuned, by
setting up our own DNSSEC policy with customized parameters. However, in many
cases the defaults are adequate.
At the time of this writing (mid-2020), dnssec-policy is still a
relatively new feature in BIND. Although it is the preferred
way to run DNSSEC in a zone, it is not yet able to automatically implement
all the features that are available
with a more “hands-on” approach to signing and key maintenance. For this
reason, we cover alternative signing techniques in
Alternate Ways of Signing a Zone.
As mentioned in Uploading Information to the Parent Zone,
the format of the information uploaded to your parent zone is dictated
by your parent zone administrator. The two main formats are:
DS record format
DNSKEY format
Check with your parent zone to see which format they require.
But how can you get each of the formats from your existing data?
When named turned on automatic
DNSSEC maintenance, essentially the first thing it did was to create
the DNSSEC keys and put them in the directory you specified in the
configuration file. If you look in that directory, you will see three
files with names like Kexample.com.+013+10376.key,
Kexample.com.+013+10376.private, and
Kexample.com.+013+10376.state. The one we are interested in is the
one with the .key suffix, which contains the zone’s public key. (The
other files contain the zone’s private key and the DNSSEC state
associated with the key.) This public key is used to generate the information we
need to pass to the parent.
Below is an example of a DS record format generated from the KSK we
created earlier (Kexample.com.+013+10376.key):
# cd /etc/binddnssec-dsfromkeyKexample.com.+013+10376.keyexample.com.INDS10376132B92E22CAE0B41430EC38D3F7EDF1183C3A94F4D4748569250C15EE33B8312EF0
Some registrars ask their customers to manually specify the types of algorithm
and digest used. In this example, 13 represents the algorithm used, and
2 represents the digest type (SHA-256). The key tag or key ID is 10376.
The key itself is easy to find (it’s difficult to miss that long
base64 string) in the file.
# cd /etc/bind# cat Kexample.com.+013+10376.key;Thisisakey-signingkey,keyid10376,forexample.com.;Created:20200407150255(TueApr716:02:552020);Publish:20200407150255(TueApr716:02:552020);Activate:20200407150255(TueApr716:02:552020)example.com.3600INDNSKEY2573136saiq99qDB...dqp+o0dw==
The remainder of this section describes the contents of a custom DNSSEC
policy. Advanced Discussions describes the concepts
involved here and the pros and cons of choosing particular values. If
you are not already familiar with DNSSEC, it may be worth reading that chapter
first.
Setting up your own DNSSEC policy means that you must include a
dnssec-policy clause in the zone file. This sets values for the
various parameters that affect the signing of zones and the rolling of
keys. The following is an example of such a clause:
The name must be specified. As each zone can use a different policy,
named needs to be able to distinguish between policies. This is
done by giving each policy a name, such as standard in the above
example.
The keys clause lists all keys that should be in the zone, along
with their associated parameters. In this example, we are using the
conventional KSK/ZSK split, with the KSK changed every year and the
ZSK changed every two months (the default DNSSEC policy sets a
CSK that is never changed). Keys are created using the
ECDSAPS256SHA256 algorithm; each KSK/ZSK pair must have the same
algorithm. A CSK combines the functionality of a ZSK and a KSK.
The parameters ending in -ttl are, as expected, the TTLs of the
associated records. Remember that during a key rollover,
we have to wait for records to expire from caches? The values
here tell BIND 9 the maximum amount of time it has to wait for this to
happen. Values can be set for the DNSKEY records in your zone, the
non-DNSKEY records in your zone, and the DS records in the parent
zone.
Another set of time-related parameters are those ending in
-propagation-delay. These tell BIND how long it takes for a
change in zone contents to become available on all secondary servers.
(This may be non-negligible: for example, if a large zone is
transferred over a slow link.)
The policy also sets values for the various signature parameters: how
long the signatures on the DNSKEY and non-DNSKEY records are valid,
and how often BIND should re-sign the zone.
The parameters ending in -safety are there to give
you a bit of leeway in case a key roll doesn’t go to plan. When
introduced into the zone, the publish-safety time is the amount
of additional time, over and above that calculated from the other
parameters, during which the new key is in the zone but before BIND starts
to sign records with it. Similarly, the retire-safety is the
amount of additional time, over and above that calculated from the
other parameters, during which the old key is retained in the zone before
being removed.
Finally, the purge-keys option allows you to clean up key files
automatically after a period of time. If a key has been removed from the
zone, this option will determine how long its key files will be retained
on disk.
(You do not have to specify all the items listed above in your policy
definition. Any that are not set simply take the default value.)
Usually, the exact timing of a key roll, or how long a signature remains
valid, is not critical. For this reason, err on the side of caution when
setting values for the parameters. It is better to have an operation
like a key roll take a few days longer than absolutely required, than it
is to have a quick key roll but have users get validation failures
during the process.
Having defined a new policy called “standard”, we now need to tell
named to use it. We do this by adding a dnssec-policystandard;
statement to the configuration file. Like many other configuration
statements, it can be placed in the options statement (thus applying
to all zones on the server), a view statement (applying to all zones
in the view), or a zone statement (applying only to that zone). In
this example, we’ll add it to the zone statement:
Zone data is signed and the parent zone has published your DS records:
at this point your zone is officially secure. When other
validating resolvers look up information in your zone, they are able to
follow the 12-step process as described in
How Does DNSSEC Change DNS Lookup (Revisited)? and verify the
authenticity and integrity of the answers.
There is not that much left for you, as the DNS administrator, to do on
an ongoing basis. Whenever you update your zone, BIND automatically
re-signs your zone with new RRSIG and NSEC/NSEC3 records, and even
increments the serial number for you. If you choose to split your keys
into a KSK and ZSK, the rolling of the ZSK is completely automatic.
Rolling of a KSK or CSK may require some manual intervention, though,
so let’s examine two more DNSSEC-related resource records, CDS and CDNSKEY.
Passing the DS record to the organization running the parent zone has
always been recognized as a bottleneck in the key rollover process. To
automate the process, the CDS and CDNSKEY resource records were
introduced.
The CDS and CDNSKEY records are identical to the DS and DNSKEY records,
except in the type code and the name. When such a record appears in the
child zone, it is a signal to the parent that it should update the DS it
has for that zone. In essence, when the parent notices
the presence of the CDS and/or CDNSKEY record(s) in the
child zone, it checks these records to verify that they are
signed by a valid key for the zone. If the record(s) successfully
validate, the parent zone’s DS RRset for the child zone is changed to
correspond to the CDS (or CDNSKEY) records. (For more
information on how the signaling works and the issues surrounding it,
please refer to RFC 7344 and RFC 8078.)
Once the zone is signed, the only required manual tasks are
to monitor KSK or CSK key rolls and pass the new DS record to the
parent zone. However, if the parent can process CDS or CDNSKEY records,
you may not even have to do that 6.
When the time approaches for the roll of a KSK or CSK, BIND adds a
CDS and a CDNSKEY record for the key in question to the apex of the
zone. If your parent zone supports polling for CDS/CDNSKEY records, they
are uploaded and the DS record published in the parent - at least ideally.
If BIND is configured with parental-agents, it will check for the DS
presence. Let’s look at the following configuration excerpt:
BIND will check for the presence of the DS record in the parent zone by querying
its parental agents (defined in RFC 7344 to be the entities that the child
zone has a relationship with to change its delegation information). In the
example above, The zone example.net is configured with two parental agents,
at the addresses 10.53.0.11 and 10.53.0.12. These addresses are used as an
example only. Both addresses will have to respond with a DS RRset that
includes the DS record identifying the key that is being rolled. If one or
both don’t have the DS included yet the rollover is paused, and the check for
DS presence is retried after an hour. The same applies for DS withdrawal.
Alternatively, you can use the rndc tool to tell named that the DS
record has been published or withdrawn. For example:
# rndc dnssec -checkds published example.net
If your parent zone doesn’t support CDS/CDNSKEY, you will have to supply
the DNSKEY or DS record to the parent zone manually when a new KSK appears in
your zone, presumably using the same mechanism you used to upload the
records for the first time. Again, you need to use the rndc tool
to tell named that the DS record has been published.
For security reasons, a parent zone that supports CDS/CDNSKEY may require
the DS record to be manually uploaded when we first sign the zone.
Until our zone is signed, the parent cannot be sure that a CDS or CDNSKEY
record it finds by querying our zone really comes from our zone; thus, it
needs to use some other form of secure transfer to obtain the information.
Although use of the automatic dnssec-policy is the preferred way to sign zones in
BIND, there are occasions where a more manual approach may be
needed, such as when external hardware is used to
generate and sign the zone. dnssec-policy does not currently support
the use of external hardware, so if your security policy requires it, you
need to use one of the methods described here.
The idea of DNSSEC was first discussed in the 1990s and has been
extensively developed over the intervening years. BIND has tracked the
development of this technology, often being the first name server
implementation to introduce new features. However, for compatibility reasons, BIND
retained older ways of doing things even when new ways were added. This
particularly applies to signing and maintaining zones, where different
levels of automation are available.
The following is a list of the available methods of signing in BIND, in the
order that they were introduced - and in order of decreasing
complexity.
Manual
“Manual” signing was the first method to be introduced into BIND and
its name describes it perfectly: the user needs to do everything. In the
more-automated methods, you load an unsigned zone file into
named, which takes care of signing it. With manual signing, you
have to provide a signed zone for named to serve.
In practice, this means creating an unsigned zone file as usual, then
using the BIND-provided tools dnssec-keygen to create the keys
and dnssec-signzone to sign the zone. The signed zone is stored
in another file and is the one you tell BIND to load. To
update the zone (for example, to add a resource record), you update the
unsigned zone, re-sign it, and tell named to load the updated
signed copy. The same goes for refreshing signatures or rolling keys;
the user is responsible for providing the signed zone served by
named. (In the case of rolling keys, you are also responsible for
ensuring that the keys are added and removed at the correct times.)
Why would you want to sign your zone this way? You probably
wouldn’t in the normal course of events, but as there may be
circumstances in which it is required, the scripts have been left in
the BIND distribution.
Semi-Automatic
The first step in DNSSEC automation came with BIND 9.7, when the
auto-dnssec option was added. This causes named to
periodically search the directory holding the key files (see
Generate Keys for a description) and to
use the information in them to both add and remove keys and sign the
zone.
Use of auto-dnssec alone requires that the zone be dynamic,
something not suitable for a number of situations, so BIND 9.9 added the
inline-signing option. With this, named essentially keeps the
signed and unsigned copies of the zone separate. The signed zone is
created from the unsigned one using the key information; when the
unsigned zone is updated and the zone reloaded, named detects the
changes and updates the signed copy of the zone.
This mode of signing has been termed “semi-automatic” in this
document because keys still have to be manually created (and deleted
when appropriate). Although not an onerous task, it is still
additional work.
Why would anyone want to use this
method when fully automated ones are available? At the time of
this writing (mid-2020), the fully automatic methods cannot handle all scenarios,
particularly that of having a single key shared among multiple
zones. They also do not handle keys stored in Hardware Security
Modules (HSMs), which are briefly covered in
Hardware Security Modules (HSMs).
Fully Automatic with dnssec-keymgr
The next step in the automation of DNSSEC operations came with BIND
9.11, which introduced the dnssec-keymgr utility. This is a
separate program and is expected to be run on a regular basis
(probably via cron). It reads a DNSSEC policy from its
configuration file and reads timing information from the DNSSEC key
files. With this information it creates new key files with timing
information in them consistent with the policy. named is run as
usual, picking up the timing information in the key files to
determine when to add and remove keys, and when to sign with them.
In BIND 9.17.0 and later, this method of handling DNSSEC
policies has been replaced by the dnssec-policy statement in the
configuration file.
Fully Automatic with dnssec-policy
Introduced a BIND 9.16, dnssec-policy replaces dnssec-keymgr from BIND
9.17 onwards and avoids the need to run a separate program. It also
handles the creation of keys if a zone is added (dnssec-keymgr
requires an initial key) and deletes old key files as they are
removed from the zone. This is the method described in
Easy-Start Guide for Signing Authoritative Zones.
We now look at some of these methods in more detail. We cover
semi-automatic signing first, as that contains a lot of useful
information about keys and key timings. We then describe what
dnssec-keymgr adds to semi-automatic signing. After that, we
touch on fully automatic signing with dnssec-policy. Since this has
already been described in
Easy-Start Guide for Signing Authoritative Zones, we will just
mention a few additional points. Finally, we briefly describe manual signing.
As noted above, the term semi-automatic signing has been used in this
document to indicate the mode of signing enabled by the auto-dnssec
and inline-signing keywords. named signs the zone without any
manual intervention, based purely on the timing information in the
DNSSEC key files. The files, however, must be created manually.
By appropriately setting the key parameters and the timing information
in the key files, you can implement any DNSSEC policy you want for your
zones. But why manipulate the key information yourself rather than rely
on dnssec-keymgr or dnssec-policy to do it for you? The answer
is that semi-automatic signing allows you to do things that, at the time of this writing
(mid-2020), are currently not possible with one of the key managers: for
example, the ability to use an HSM to store keys, or the ability to use
the same key for multiple zones.
To convert a traditional
(insecure) DNS zone to a secure one, we need to create various
additional records (DNSKEY, RRSIG, NSEC/NSEC3) and, as with
fully automatic signing, to upload verifiable information (such as a DS
record) to the parent zone to complete the chain of trust.
Note
Again, we assume all configuration files, key
files, and zone files are stored in /etc/bind, and most examples
show commands run
as the root user. This may not be ideal, but the point is not
to distract from what is important here: learning how to sign
a zone. There are many best practices for deploying a more secure
BIND installation, with techniques such as jailed process and
restricted user privileges, but those are not covered
in this document. We trust you, a responsible DNS
administrator, to take the necessary precautions to secure your
system.
For our examples below, we work with the assumption that
there is an existing insecure zone example.com that we are
converting to a secure version. The secure version uses both a KSK
and a ZSK.
This command generates four key files in /etc/bind/keys:
Kexample.com.+013+34371.key
Kexample.com.+013+34371.private
Kexample.com.+013+00472.key
Kexample.com.+013+00472.private
The two files ending in .key are the public keys. These contain the
DNSKEY resource records that appear in the zone. The two files
ending in .private are the private keys, and contain the information
that named actually uses to sign the zone.
Of the two pairs, one is the zone-signing key (ZSK), and one is the
key-signing key (KSK). We can tell which is which by looking at the file
contents (the actual keys are shortened here for ease of display):
# catKexample.com.+013+34371.key
; This is a zone-signing key, keyid 34371, for example.com.; Created: 20200616104249 (Tue Jun 16 11:42:49 2020); Publish: 20200616104249 (Tue Jun 16 11:42:49 2020); Activate: 20200616104249 (Tue Jun 16 11:42:49 2020)example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8=# catKexample.com.+013+00472.key
; This is a key-signing key, keyid 472, for example.com.; Created: 20200616104254 (Tue Jun 16 11:42:54 2020); Publish: 20200616104254 (Tue Jun 16 11:42:54 2020); Activate: 20200616104254 (Tue Jun 16 11:42:54 2020)example.com. IN DNSKEY 257 3 13 AwEAAbCR6U...l8xPjokVU=
The first line of each file tells us what type of key it is. Also, by
looking at the actual DNSKEY record, we can tell them apart: 256 is
ZSK, and 257 is KSK.
The name of the file also tells us something
about the contents. See chapter Zone keys for more details.
Make sure that these files are readable by named and that the
.private files are not readable by anyone else.
Alternativelly, the dnssec-keyfromlabel program is used to get a key
pair from a crypto hardware device and build the key files. Its usage is
similar to dnssec-keygen.
You may remember that in the above description of this method, we said
that time information related to rolling keys is stored in the key
files. This is placed there by dnssec-keygen when the file is
created, and it can be modified using dnssec-settime. By default,
only a limited amount of timing information is included in the file, as
illustrated in the examples in the previous section.
All the dates are the same, and are the date and time that
dnssec-keygen created the key. We can use dnssec-settime to
modify the dates 7. For example, to publish this key in
the zone on 1 July 2020, use it to sign records for a year starting on
15 July 2020, and remove it from the zone at the end of July 2021, we
can use the following command:
; This is a zone-signing key, keyid 34371, for example.com.
; Created: 20200616104249 (Tue Jun 16 11:42:49 2020)
; Publish: 20200701000000 (Wed Jul 1 01:00:00 2020)
; Activate: 20200715000000 (Wed Jul 15 01:00:00 2020)
; Inactive: 20210715000000 (Thu Jul 15 01:00:00 2021)
; Delete: 20210731000000 (Sat Jul 31 01:00:00 2021)
example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8=
(The actual key is truncated here to improve readability.)
Below is a complete list of each of the metadata fields, and how each
one affects the signing of your zone:
Created: This records the date on which the key was created. It is
not used in calculations; it is useful simply for documentation
purposes.
Publish: This sets the date on which a key is to be published to the
zone. After that date, the key is included in the zone but is
not used to sign it. This allows validating resolvers to get a
copy of the new key in their cache before there are any resource
records signed with it. By default, if not specified at creation
time, this is set to the current time, meaning the key is
published as soon as named picks it up.
Activate: This sets the date on which the key is to be activated. After
that date, resource records are signed with the key. By default,
if not specified during creation time, this is set to the current
time, meaning the key is used to sign data as soon as named
picks it up.
Revoke: This sets the date on which the key is to be revoked. After that
date, the key is flagged as revoked, although it is still included in the
zone and used to sign it. This is used to notify validating
resolvers that this key is about to be removed or retired from the
zone. (This state is not used in normal day-to-day operations. See
RFC 5011 to understand the circumstances where it may be used.)
Inactive: This sets the date on which the key is to become inactive.
After that date, the key is still included in the zone, but it
is no longer used to sign it. This sets the “expiration” or “retire”
date for a key.
Delete: This sets the date on which the key is to be deleted. After that
date, the key is no longer included in the zone, but it
continues to exist on the file system or key repository.
The publication date is the date the key is introduced into the zone.
Sometime later it is activated and is used to sign resource records.
After a specified period, BIND stops using it to sign records, and at some
other specified later time it is removed from the zone.
Finally, we should note that the dnssec-keygen command supports the
same set of switches so we could have set the dates
when we created the key.
Having created the keys with the appropriate timing information, the
next step is to turn on DNSSEC signing. Below is a very simple
named.conf; in our example environment, this file is
/etc/bind/named.conf.
As described in Uploading Information to the Parent Zone, we
must now upload the new information to the parent zone. The format of the
information and how to generate it is described in
Working With the Parent Zone, although it is important to remember that you must
use the contents of the KSK file that you generated above as part of the
process.
When the DS record is published in the parent zone, your zone is fully
signed.
Finally, follow the steps in How To Test Authoritative Zones
to confirm that a query recognizes the zone as properly signed and
vouched for by the parent zone.
Once the zone is signed, it must be monitored as described
in Maintenance Tasks. However,
as the time approaches for a key roll, you must create the new key. Of
course, it is possible to create keys for the next fifty
years all at once and set the key times appropriately. Whether the
increased risk in having the private key files for future keys available
on disk offsets the overhead of having to remember to create a new key
before a rollover depends on your organization’s security policy.
dnssec-keymgr is a program supplied with BIND (versions 9.11 to
9.16) to help with key rollovers. When run, it compares the timing
information for existing keys with the defined policy, and adjusts it if
necessary. It also creates additional keys as required.
dnssec-keymgr is completely separate from named. As we will see,
the policy states a coverage period; dnssec-keymgr generates
enough key files to handle all rollovers in that period. However, it is
a good idea to schedule it to run on a regular basis; that way there is
no chance of forgetting to run it when the coverage period ends.
BIND should be set up exactly the same way as described in
Semi-Automatic Signing, i.e.,
with auto-dnssec set to maintain and inline-signing set to
true. Then a policy file must be created. The following is an
example of such a file:
As can be seen, the syntax is similar to that of the named
configuration file.
In the example above, we define a DNSSEC policy called “standard”. Keys
are created using the RSASHA256 algorithm, assigned a TTL of two hours,
and placed in the directory /etc/bind. KSKs have a key size of
4096 bits and are expected to roll once a year; the new key is added to the
zone 30 days before it becomes active, and is retained in the zone for
30 days after it is rolled. ZSKs have a key size of 2048 bits and roll
every 90 days; like the KSKs, the are added to the zone 30 days before
they are used for signing, and retained for 30 days after named
ceases signing with them.
The policy is applied to two zones, example.com and example.net.
The policy is applied unaltered to the former, but for the latter the
setting for the DNSKEY TTL has been overridden and set to 300 seconds.
To apply the policy, we need to run dnssec-keymgr. Since this does
not read the named configuration file, it relies on the presence of
at least one key file for a zone to tell it that the zone is
DNSSEC-enabled. If a key file does not already exist, we first need to create
one for each zone. We can do that either by running
dnssec-keygen to create a key file for each zone 8, or by
specifying the zones in question on the command line. Here, we do the
latter:
This creates enough key files to last for the coverage period, set in
the policy file to be one year. The script should be run on a regular
basis (probably via cron) to keep the reserve of key files topped
up. With the shortest roll period set to 90 days, every 30 days is
more than adequate.
At any time, you can check what key changes are coming up and whether
the keys and timings are correct by using dnssec-coverage. For
example, to check coverage for the next 60 days:
The -d2h and -m1d on the command line specify the maximum TTL
for the DNSKEYs and other resource records in the zone: in this example
two hours and one day, respectively. dnssec-coverage needs this
information when it checks that the zones will remain secure through key
rolls.
The latest development in DNSSEC key management appeared with BIND 9.16,
and is the full integration of key management into named. Managing
the signing process and rolling of these keys has been described in
Easy-Start Guide for Signing Authoritative Zones and is not
repeated here. A few points are worth noting, though:
The dnssec-policy statement in the named configuration file
describes all aspects of the DNSSEC policy, including the signing.
With dnssec-keymgr, this is split between two configuration files
and two programs.
The dnssec-policy statement requires to zone to use dynamic DNS,
or that inline-signing is enabled.
It is possible to manage some zones served by an instance of BIND
through dnssec-policy and others through dnssec-keymgr, but
this is not recommended. Although it should work, if you
modify the configuration files and inadvertently specify a zone to be
managed by both systems, BIND will not operate properly.
Manual signing of a zone was the first method of signing introduced into
BIND and offers, as the name suggests, no automation. The user must
handle everything: create the keys, sign the zone file with them, load
the signed zone, periodically re-sign the zone, and manage key rolls,
including interaction with the parent. A user certainly can do all this,
but why not use one of the automated methods? Nevertheless, it may
be useful for test purposes, so we cover it briefly here.
BIND 9 ships with several tools that are used in
this process, which are explained in more detail below. In all cases,
the -h option prints a full list of parameters. Note that the DNSSEC
tools require the keyset files to be in the working directory or the
directory specified by the -d option.
The first step is to create the keys as described in Generate Keys.
Then, edit the zone file to make sure the proper DNSKEY entries are included.
The public keys should be inserted into the zone file by
including the .key files using $INCLUDE statements.
Finally, use the command dnssec-signzone.
Any keyset files corresponding to secure sub-zones should be
present. The zone signer generates NSEC, NSEC3, and RRSIG
records for the zone, as well as DS for the child zones if
-g is specified. If
-g is not specified, then DS RRsets for the
secure child zones need to be added manually.
By default, all zone keys which have an available private key are used
to generate signatures. The following command signs the zone, assuming
it is in a file called zone.child.example, using manually specified keys:
# cd/etc/bind/keys/example.com/
# dnssec-signzone-t-NINCREMENT-oexample.com-f/etc/bind/db/example.com.signed.db\/etc/bind/db/example.com.dbKexample.com.+013+17694.keyKexample.com.+013+06817.key
Verifying the zone using the following algorithms: ECDSAP256SHA256.Zone fully signed:Algorithm: ECDSAP256SHA256: KSKs: 1 active, 0 stand-by, 0 revoked ZSKs: 1 active, 0 stand-by, 0 revoked/etc/bind/db/example.com.signed.dbSignatures generated: 17Signatures retained: 0Signatures dropped: 0Signatures successfully verified: 0Signatures unsuccessfully verified: 0Signing time in seconds: 0.046Signatures per second: 364.634Runtime in seconds: 0.055
The -o switch explicitly defines the domain name (example.com in
this case), while the -f switch specifies the output file name. The second line
has three parameters: the unsigned zone name
(/etc/bind/db/example.com.db), the ZSK file name, and the KSK file name. This
also generates a plain text file /etc/bind/db/example.com.signed.db,
which can be manually verified for correctness.
dnssec-signzone also produces keyset and dsset files. These are used
to provide the parent zone administrators with the DNSKEY records (or their
corresponding DS records) that are the secure entry point to the zone.
Finally, you’ll need to update named.conf to load the signed version
of the zone, which looks something like this:
zone "example.com" IN {
type primary;
file "db/example.com.signed.db";
};
Once the rndcreconfig command is issued, BIND serves a signed
zone. The file dsset-example.com (created by dnssec-signzone
when it signed the example.com zone) contains the DS record for the
zone’s KSK. You will need to pass that to the administrator of the parent
zone, to be placed in the zone.
Since this is a manual process, you will need to re-sign periodically,
as well as every time the zone
data changes. You will also need to manually roll the keys by adding and
removing DNSKEY records (and interacting with the parent) at the
appropriate times.
In this chapter, we cover some basic troubleshooting
techniques, some common DNSSEC symptoms, and their causes and solutions. This
is not a comprehensive “how to troubleshoot any DNS or DNSSEC problem”
guide, because that could easily be an entire book by itself.
The first step in troubleshooting DNS or DNSSEC should be to
determine the query path. Whenever you are working with a DNS-related issue, it is
always a good idea to determine the exact query path to identify the
origin of the problem.
End clients, such as laptop computers or mobile phones, are configured
to talk to a recursive name server, and the recursive name server may in
turn forward requests on to other recursive name servers before arriving at the
authoritative name server. The giveaway is the presence of the
Authoritative Answer (aa) flag in a query response: when present, we know we are talking
to the authoritative server; when missing, we are talking to a recursive
server. The example below shows an answer to a query for
www.example.com without the Authoritative Answer flag:
$ dig @10.53.0.3 www.example.com A
; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.com a
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62714
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: c823fe302625db5b010000005e722b504d81bb01c2227259 (good)
;; QUESTION SECTION:
;www.example.com. IN A
;; ANSWER SECTION:
www.example.com. 60 IN A 10.1.0.1
;; Query time: 3 msec
;; SERVER: 10.53.0.3#53(10.53.0.3)
;; WHEN: Wed Mar 18 14:08:16 GMT 2020
;; MSG SIZE rcvd: 88
Not only do we not see the aa flag, we see an ra
flag, which indicates Recursion Available. This indicates that the
server we are talking to (10.53.0.3 in this example) is a recursive name
server: although we were able to get an answer for
www.example.com, we know that the answer came from somewhere else.
If we query the authoritative server directly, we get:
$ dig @10.53.0.2 www.example.com A
; <<>> DiG 9.16.0 <<>> @10.53.0.2 www.example.com a
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39542
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
...
The aa flag tells us that we are now talking to the
authoritative name server for www.example.com, and that this is not a
cached answer it obtained from some other name server; it served this
answer to us right from its own database. In fact,
the Recursion Available (ra) flag is not present, which means this
name server is not configured to perform recursion (at least not for
this client), so it could not have queried another name server to get
cached results.
After determining the query path, it is necessary to
determine whether the problem is actually related to DNSSEC
validation. You can use the +cd flag in dig to disable
validation, as described in
How Do I Know I Have a Validation Problem?.
When there is indeed a DNSSEC validation problem, the visible symptoms,
unfortunately, are very limited. With DNSSEC validation enabled, if a
DNS response is not fully validated, it results in a generic
SERVFAIL message, as shown below when querying against a recursive name
server at 192.168.1.7:
Usually, this level of error logging is sufficient.
Debug logging, described in
BIND DNSSEC Debug Logging, gives information on how
to get more details about why DNSSEC validation may have
failed.
A word of caution: before you enable debug logging, be aware that this
may dramatically increase the load on your name servers. Enabling debug
logging is thus not recommended for production servers.
With that said, sometimes it may become necessary to temporarily enable
BIND debug logging to see more details of how and whether DNSSEC is
validating. DNSSEC-related messages are not recorded in syslog by default,
even if query log is enabled; only DNSSEC errors show up in syslog.
The example below shows how to enable debug level 3 (to see full DNSSEC
validation messages) in BIND 9 and have it sent to syslog:
After turning on debug logging and restarting BIND, a large
number of log messages appear in
syslog. The example below shows the log messages as a result of
successfully looking up and validating the domain name ftp.isc.org.
Similar to lame delegation in traditional DNS, security lameness refers to the
condition when the parent zone holds a set of DS records that point to
something that does not exist in the child zone. As a result,
the entire child zone may “disappear,” having been marked as bogus by
validating resolvers.
Below is an example attempting to resolve the A record for a test domain
name www.example.net. From the user’s perspective, as described in
How Do I Know I Have a Validation Problem?, only a SERVFAIL
message is returned. On the validating resolver, we see the
following messages in syslog:
This gives us a hint that it is a broken trust chain issue. Let’s take a
look at the DS records that are published for the zone (with the keys
shortened for ease of display):
Next, we query for the DNSKEY and RRSIG of example.net to see if
there’s anything wrong. Since we are having trouble validating, we
can use the +cd option to temporarily disable checking and return
results, even though they do not pass the validation tests. The
+multiline option tells dig to print the type, algorithm type,
and key id for DNSKEY records. Again,
some long strings are shortened for ease of display:
Here is the problem: the parent zone is telling the world that
example.net is using the key 14956, but the authoritative server
indicates that it is using keys 27247 and 35328. There are several
potential causes for this mismatch: one possibility is that a malicious
attacker has compromised one side and changed the data. A more likely
scenario is that the DNS administrator for the child zone did not upload
the correct key information to the parent zone.
In DNSSEC, every record comes with at least one RRSIG, and each RRSIG
contains two timestamps: one indicating when it becomes valid, and
one when it expires. If the validating resolver’s current system time does
not fall within the two RRSIG timestamps, error messages
appear in the BIND debug log.
The example below shows a log message when the RRSIG appears to have
expired. This could mean the validating resolver system time is
incorrectly set too far in the future, or the zone administrator has not
kept up with RRSIG maintenance.
The log below shows that the RRSIG validity period has not yet begun. This could mean
the validation resolver’s system time is incorrectly set too far in the past, or
the zone administrator has incorrectly generated signatures for this
domain name.
This is a simple yet common issue. If the key files are present but
unreadable by named for some reason, the syslog returns clear error
messages, as shown below:
However, if no keys are found, the error is not as obvious. Below shows
the syslog messages after executing rndcreload with the key files missing from the key directory:
This happens to look exactly the same as if the keys were present and
readable, and appears to indicate that named loaded the keys and signed the zone. It
even generates the internal (raw) files:
# cd /etc/bind/db# lsexample.com.dbexample.com.db.jbkexample.com.db.signed
If named really loaded the keys and signed the zone, you should see
the following files:
# cd /etc/bind/db# lsexample.com.dbexample.com.db.jbkexample.com.db.signedexample.com.db.signed.jnl
So, unless you see the *.signed.jnl file, your zone has not been
signed.
In most cases, you never need to explicitly configure trust
anchors. named supplies the current root trust anchor and,
with the default setting of dnssec-validation, updates it on the
infrequent occasions when it is changed.
However, in some circumstances you may need to explicitly configure
your own trust anchor. As we saw in the Trust Anchors
section, whenever a DNSKEY is received by the validating resolver, it is
compared to the list of keys the resolver explicitly trusts to see if
further action is needed. If the two keys match, the validating resolver
stops performing further verification and returns the answer(s) as
validated.
But what if the key file on the validating resolver is misconfigured or
missing? Below we show some examples of log messages when things are not
working properly.
First of all, if the key you copied is malformed, BIND does not even
start and you will likely find this error message in syslog:
If the key is a valid base64 string but the key algorithm is incorrect,
or if the wrong key is installed, the first thing you will notice is
that virtually all of your DNS lookups result in SERVFAIL, even when
you are looking up domain names that have not been DNSSEC-enabled. Below
shows an example of querying a recursive server 10.53.0.3:
$ dig @10.53.0.3 www.example.com. A
; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.org A +dnssec
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 29586
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: ee078fc321fa1367010000005e73a58bf5f205ca47e04bed (good)
;; QUESTION SECTION:
;www.example.org. IN A
BIND 9.11 introduced Negative Trust Anchors (NTAs) as a means to
temporarily disable DNSSEC validation for a zone when you know that
the zone’s DNSSEC is misconfigured.
The list of currently configured NTAs can also be examined using
rndc, e.g.:
$ rndc nta -dump
example.com/_default: expiry 19-Mar-2020 19:57:42.000
The default lifetime of an NTA is one hour, although by default, BIND
polls the zone every five minutes to see if the zone correctly
validates, at which point the NTA automatically expires. Both the
default lifetime and the polling interval may be configured via
named.conf, and the lifetime can be overridden on a per-zone basis
using the -lifetimeduration parameter to rndcnta. Both timer
values have a permitted maximum value of one week.
BIND includes a tool called nsec3hash that runs through the same
steps as a validating resolver, to generate the correct hashed name
based on NSEC3PARAM parameters. The command takes the following
parameters in order: salt, algorithm, iterations, and domain. For
example, if the salt is 1234567890ABCDEF, hash algorithm is 1, and
iteration is 10, to get the NSEC3-hashed name for www.example.com we
would execute a command like this:
Signature Validity Periods and Zone Re-Signing Intervals
In How Are Answers Verified?, we saw that record signatures
have a validity period outside of which they are not valid. This means
that at some point, a signature will no longer be valid and a query for
the associated record will fail DNSSEC validation. But how long should a
signature be valid for?
The maximum value for the validity period should be determined by the impact of a
replay attack: if this is low, the period can be long; if high,
the period should be shorter. There is no “right” value, but periods of
between a few days to a month are common.
Deciding a minimum value is probably an easier task. Should something
fail (e.g., a hidden primary distributing to secondary servers that
actually answer queries), how long will it take before the failure is
noticed, and how long before it is fixed? If you are a large 24x7
operation with operators always on-site, the answer might be less than
an hour. In smaller companies, if the failure occurs
just after everyone has gone home for a long weekend, the answer might
be several days.
Again, there are no “right” values - they depend on your circumstances. The
signature validity period you decide to use should be a value between
the two bounds. At the time of this writing (mid-2020), the default policy used by BIND
sets a value of 14 days.
To keep the zone valid, the signatures must be periodically refreshed
since they expire - i.e., the zone must be periodically
re-signed. The frequency of the re-signing depends on your network’s
individual needs. For example, signing puts a load on your server, so if
the server is very highly loaded, a lower re-signing frequency is better. Another
consideration is the signature lifetime: obviously the intervals between
signings must not be longer than the signature validity period. But if
you have set a signature lifetime close to the minimum (see above), the
signing interval must be much shorter. What would happen if the system
failed just before the zone was re-signed?
Again, there is no single “right” answer; it depends on your circumstances. The
BIND 9 default policy sets the signature refresh interval to 5 days.
How do you prove that something does not exist? This zen-like question
is an interesting one, and in this section we provide an overview
of how DNSSEC solves the problem.
Why is it even important to have authenticated denial of existence in DNS?
Couldn’t we just send back “hey, what you asked for does not exist,”
and somehow generate a digital signature to go with it, proving it
really is from the correct authoritative source? Aside from the technical
challenge of signing something that doesn’t exist, this solution has flaws, one of
which is it gives an attacker a way to create the appearance of denial
of service by replaying this message on the network.
Let’s use a little story, told three different ways, to
illustrate how proof of nonexistence works. In our story, we run a small
company with three employees: Alice, Edward, and Susan. For reasons that
are far too complicated to go into, they don’t have email accounts;
instead, email for them is sent to a single account and a nameless
intern passes the message to them. The intern has access to our private
DNSSEC key to create signatures for their responses.
If we followed the approach of giving back the same answer no matter
what was asked, when people emailed and asked for the message to be
passed to “Bob,” our intern would simply answer “Sorry, that person
doesn’t work here” and sign this message. This answer could be validated
because our intern signed the response with our private DNSSEC key.
However, since the signature doesn’t change, an attacker could record
this message. If the attacker were able to intercept our email, when the next
person emailed asking for the message to be passed to Susan, the attacker
could return the exact same message: “Sorry, that person doesn’t work
here,” with the same signature. Now the attacker has successfully fooled
the sender into thinking that Susan doesn’t work at our company, and
might even be able to convince all senders that no one works at this
company.
To solve this problem, two different solutions were created. We will
look at the first one, NSEC, next.
The NSEC record is used to prove that something does not exist, by
providing the name before it and the name after it. Using our tiny
company example, this would be analogous to someone sending an email for
Bob and our nameless intern responding with with: “I’m sorry, that
person doesn’t work here. The name before the location where ‘Bob’
would be is Alice, and the name after that is Edward.” Let’s say
another email was received for a
non-existent person, this time Oliver; our intern would respond “I’m
sorry, that person doesn’t work here. The name before the location
where ‘Oliver’ would be is Edward,
and the name after that is Susan.” If another sender asked for Todd, the
answer would be: “I’m sorry, that person doesn’t work here. The name
before the location where ‘Todd’ would be is Susan, and there are no
other names after that.”
What if the attacker tried to use the same replay method described
earlier? If someone sent an email for Edward, none of the four answers
would fit. If attacker replied with message #2, “I’m sorry, that person
doesn’t work here. The name before it is Alice, and the name after it is
Edward,” it is obviously false, since “Edward” is in the response; and the same
goes for #3, Edward and Susan. As for #1 and #4, Edward does not fall in
the alphabetical range before Alice or after Susan, so the sender can logically deduce
that it was an incorrect answer.
When BIND signs your zone, the zone data is automatically sorted on
the fly before generating NSEC records, much like how a phone directory
is sorted.
The NSEC record allows for a proof of non-existence for record types. If
you ask a signed zone for a name that exists but for a record type that
doesn’t (for that name), the signed NSEC record returned lists all of
the record types that do exist for the requested domain name.
NSEC records can also be used to show whether a record was generated as
the result of a wildcard expansion. The details of this are not
within the scope of this document, but are described well in
RFC 7129.
Unfortunately, the NSEC solution has a few drawbacks, one of which is
trivial “zone walking.” In our story, a curious person can keep sending emails, and
our nameless, gullible intern keeps divulging information about our
employees. Imagine if the sender first asked: “Is Bob there?” and
received back the names Alice and Edward. Our sender could then email
again: “Is Edwarda there?”, and will get back Edward and Susan. (No,
“Edwarda” is not a real name. However, it is the first name
alphabetically after “Edward” and that is enough to get the intern to reply
with a message telling us the next valid name after Edward.) Repeat the
process enough times and the person sending the emails eventually
learns every name in our company phone directory. For many of you, this
may not be a problem, since the very idea of DNS is similar to a public
phone book: if you don’t want a name to be known publicly, don’t put it
in DNS! Consider using DNS views (split DNS) and only display your
sensitive names to a select audience.
The second potential drawback of NSEC is a bigger zone file and memory consumption;
there is no opt-out mechanism for insecure child zones, so each name
in the zone will get an additional NSEC record and a RRSIG record to go with
it. In practice this is a problem only for parent-zone operators dealing with
mostly insecure child zones, such as com.. To learn more about opt-out,
please see NSEC3 Opt-Out.
NSEC3 adds two additional features that NSEC does not have:
It offers no easy zone enumeration.
It provides a mechanism for the parent zone to exclude insecure
delegations (i.e., delegations to zones that are not signed) from the
proof of non-existence.
Recall that in NSEC we provided a range of
names to prove that something does not exist. But as it turns
out, even disclosing these ranges of names becomes a problem: this made
it very easy for the curious-minded to look at our entire zone. Not
only that, unlike a zone transfer, this “zone walking” is more
resource-intensive. So how do we disclose something without actually disclosing
it?
The answer is actually quite simple: hashing functions, or one-way
hashes. Without going into many details, think of it like a magical meat
grinder. A juicy piece of ribeye steak goes in one end, and out comes a
predictable shape and size of ground meat (hash) with a somewhat unique
pattern. No matter how hard you try, you cannot turn the ground meat
back into the ribeye steak: that’s what we call a one-way hash.
NSEC3 basically runs the names through a one-way hash before giving them
out, so the recipients can verify the non-existence without any
knowledge of the other names in the zone.
So let’s tell our little story for the third time, this
time with NSEC3. In this version, our intern is not given a list of actual
names; he is given a list of “hashed” names. So instead of Alice,
Edward, and Susan, the list he is given reads like this (hashes
shortened for easier reading):
Then, an email is received for Bob again. Our intern takes the name Bob
through a hash function, and the result is L8J2…, so he replies: “I’m
sorry, that person doesn’t work here. The name before that is JKMA…,
and the name after that is NTQ0…”. There, we proved Bob doesn’t exist,
without giving away any names! To put that into proper NSEC3 resource
records, they would look like this (again, hashes shortened for
ease of display):
Just because we employed one-way hash functions does not mean there is
no way for a determined individual to figure out our zone data.
Most names published in the DNS are rarely secret or unpredictable. They are
published to be memorable, used and consumed by humans. They are often recorded
in many other network logs such as email logs, certificate transparency logs,
web page links, intrusion detection systems, malware scanners, email archives,
etc. Many times a simple dictionary of commonly used domain-name prefixes
(www, mail, imap, login, database, etc.) can be used to quickly reveal a large
number of labels within a zone. Additionally, if an adversary really wants to
expend significant CPU resources to mount an offline dictionary attack on a
zone’s NSEC3 chain, they will likely be able to find most of the “guessable”
names despite any level of hashing.
Also, it is still possible to gather all of our NSEC3 records and hashed
names and perform an offline brute-force attack by trying all
possible combinations to figure out what the original name is. In our
meat-grinder analogy, this would be like someone
buying all available cuts of meat and grinding them up at home using
the same model of meat grinder, and comparing the output with the meat
you gave him. It is expensive and time-consuming (especially with
real meat), but like everything else in cryptography, if someone has
enough resources and time, nothing is truly private forever. If you
are concerned about someone performing this type of attack on your
zone data, use some of the special techniques described in RFC 4470.
Before we dive into the details of NSEC3 parametrization, please note:
the defaults should not be changed without a strong justification and a full
understanding of the potential impact.
The above NSEC3 examples used four parameters: 1, 0, 0, and
zero-length salt. 1 represents the algorithm, 0 represents the opt-out
flag, 0 represents the number of additional iterations, and - is the
salt. Let’s look at how each one can be configured:
Iterations defines the number of _additional_ times to
apply the algorithm when generating an NSEC3 hash. More iterations
consume more resources for both authoritative servers and validating
resolvers. The considerations here are similar to those seen in
Key Sizes, of security versus resources.
Warning
Do not use values higher than zero. A value of zero provides one round
of SHA-1 hashing and protects from non-determined attackers.
A greater number of additional iterations causes interoperability problems
and opens servers to CPU-exhausting DoS attacks, while providing
only doubtful security benefits.
First things first: For most DNS administrators who do not manage a huge number
of insecure delegations, the NSEC3 opt-out featuere is not relevant.
Opt-out allows for blocks of unsigned delegations to be covered by a single NSEC3
record. In other words, use of the opt-out allows large registries to only sign as
many NSEC3 records as there are signed DS or other RRsets in the zone; with
opt-out, unsigned delegations do not require additional NSEC3 records. This
sacrifices the tamper-resistance proof of non-existence offered by NSEC3 in
order to reduce memory and CPU overheads, and decreases the effectiveness of the cache
(RFC 8198).
Why would that ever be desirable? If a significant number of delegations
are not yet securely delegated, meaning they lack DS records and are still
insecure or unsigned, generating DNSSEC records for all their NS records
might consume lots of memory and is not strictly required by the child zones.
This resource-saving typically makes a difference only for huge zones like com..
Imagine that you are the operator of busy top-level domains such as com.,
with millions of insecure delegated domain names.
As of mid-2022, around 3% of all com. zones are signed. Basically,
without opt-out, with 1,000,000 delegations, only 30,000 of which are secure, you
still have to generate NSEC RRsets for the other 970,000 delegations; with
NSEC3 opt-out, you will have saved yourself 970,000 sets of records.
In contrast, for a small zone the difference is operationally negligible
and the drawbacks outweigh the benefits.
If NSEC3 opt-out is truly essential for a zone, the following
configuration can be added to dnssec-policy; for example, to create an
NSEC3 chain using the SHA-1 hash algorithm, with the opt-out flag,
no additional iterations, and no extra salt, use:
Contrary to popular belief, adding salt provides little value.
Each DNS zone is always uniquely salted using the zone name. Operators should
use a zero-length salt value.
The properties of this extra salt are complicated and beyond scope of this
document. For detailed description why the salt in the context of DNSSEC
provides little value please see IETF draft ietf-dnsop-nsec3-guidance version
10 section 2.4.
So which is better: NSEC or NSEC3? There is no single right
answer here that fits everyone; it comes down to a given network’s needs or
requirements.
In most cases, NSEC is a good choice for zone administrators. It
relieves the authoritative servers and resolver of the additional cryptographic
operations that NSEC3 requires, and NSEC is comparatively easier to
troubleshoot than NSEC3.
NSEC3 comes with many drawbacks and should be implemented only if zone
enumeration prevention is really needed, or when opt-out provides a
significant reduction in memory and CPU overheads (in other words, with a
huge zone with mostly insecure delegations).
Although DNSSEC
documentation talks about three types of keys, they are all the same
thing - but they have different roles. The roles are:
Zone-Signing Key (ZSK)
This is the key used to sign the zone. It signs all records in the
zone apart from the DNSSEC key-related RRsets: DNSKEY, CDS, and
CDNSKEY.
Key-Signing Key (KSK)
This is the key used to sign the DNSSEC key-related RRsets and is the
key used to link the parent and child zones. The parent zone stores a
digest of the KSK. When a resolver verifies the chain of trust it
checks to see that the DS record in the parent (which holds the
digest of a key) matches a key in the DNSKEY RRset, and that it is
able to use that key to verify the DNSKEY RRset. If it can do
that, the resolver knows that it can trust the DNSKEY resource
records, and so can use one of them to validate the other records in
the zone.
Combined Signing Key (CSK)
A CSK combines the functionality of a ZSK and a KSK. Instead of
having one key for signing the zone and one for linking the parent
and child zones, a CSK is a single key that serves both roles.
It is important to realize the terms ZSK, KSK, and CSK describe how the
keys are used - all these keys are represented by DNSKEY records. The
following examples are the DNSKEY records from a zone signed with a KSK
and ZSK:
$ dig @192.168.1.12 example.com DNSKEY
; <<>> DiG 9.16.0 <<>> @192.168.1.12 example.com dnskey +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54989
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 5258d7ed09db0d76010000005ea1cc8c672d8db27a464e37 (good)
;; QUESTION SECTION:
;example.com. IN DNSKEY
;; ANSWER SECTION:
example.com. 60 IN DNSKEY 256 3 13 (
tAeXLtIQ3aVDqqS/1UVRt9AE6/nzfoAuaT1Vy4dYl2CK
pLNcUJxME1Z//pnGXY+HqDU7Gr5HkJY8V0W3r5fzlw==
) ; ZSK; alg = ECDSAP256SHA256 ; key id = 63722
example.com. 60 IN DNSKEY 257 3 13 (
cxkNegsgubBPXSra5ug2P8rWy63B8jTnS4n0IYSsD9eW
VhiyQDmdgevKUhfG3SE1wbLChjJc2FAbvSZ1qk03Nw==
) ; KSK; alg = ECDSAP256SHA256 ; key id = 42933
… and a zone signed with just a CSK:
$ dig @192.168.1.13 example.com DNSKEY
; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com dnskey +multiline
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22628
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: bf19ee914b5df46e010000005ea1cd02b66c06885d274647 (good)
;; QUESTION SECTION:
;example.com. IN DNSKEY
;; ANSWER SECTION:
example.com. 60 IN DNSKEY 257 3 13 (
p0XM6AJ68qid2vtOdyGaeH1jnrdk2GhZeVvGzXfP/PNa
71wGtzR6jdUrTbXo5Z1W5QeeJF4dls4lh4z7DByF5Q==
) ; KSK; alg = ECDSAP256SHA256 ; key id = 1231
The only visible difference between the records (apart from the key data
itself) is the value of the flags fields; this is 256
for a ZSK and 257 for a KSK or CSK. Even then, the flags field is only a
hint to the software using it as to the role of the key: zones can be
signed by any key. The fact that a CSK and KSK both have the same flags
emphasizes this. A KSK usually only signs the DNSSEC key-related RRsets
in a zone, whereas a CSK is used to sign all records in the zone.
The original idea of separating the function of the key into a KSK and
ZSK was operational. With a single key, changing it for any reason is
“expensive,” as it requires interaction with the parent zone
(e.g., uploading the key to the parent may require manual interaction
with the organization running that zone). By splitting it, interaction
with the parent is required only if the KSK is changed; the ZSK can be
changed as often as required without involving the parent.
The split also allows the keys to be of different lengths. So the ZSK,
which is used to sign the record in the zone, can be of a (relatively)
short length, lowering the load on the server. The KSK, which is used
only infrequently, can be of a much longer length. The relatively
infrequent use also allows the private part of the key to be stored in a
way that is more secure but that may require more overhead to access, e.g., on
an HSM (see Hardware Security Modules (HSMs)).
In the early days of DNSSEC, the idea of splitting the key went more or
less unchallenged. However, with the advent of more powerful computers
and the introduction of signaling methods between the parent and child
zones (see The CDS and CDNSKEY Resource Records), the advantages of a ZSK/KSK split are
less clear and, for many zones, a single key is all that is required.
As with many questions related to the choice of DNSSEC policy, the
decision on which is “best” is not clear and depends on your circumstances.
There are three algorithm choices for DNSSEC as of this writing
(mid-2020):
RSA
Elliptic Curve DSA (ECDSA)
Edwards Curve Digital Security Algorithm (EdDSA)
All are supported in BIND 9, but only RSA and ECDSA (specifically
RSASHA256 and ECDSAP256SHA256) are mandatory to implement in DNSSEC.
However, RSA is a little long in the tooth, and ECDSA/EdDSA are emerging
as the next new cryptographic standards. In fact, the US federal
government recommended discontinuing RSA use altogether by September 2015
and migrating to using ECDSA or similar algorithms.
For now, use ECDSAP256SHA256 but keep abreast of developments in this
area. For details about rolling over DNSKEYs to a new algorithm, see
Algorithm Rollovers.
If using RSA keys, the choice of key sizes is a classic issue of finding
the balance between performance and security. The larger the key size,
the longer it takes for an attacker to crack the key; but larger keys
also mean more resources are needed both when generating signatures
(authoritative servers) and verifying signatures (recursive servers).
Of the two sets of keys, ZSK is used much more frequently. ZSK is used whenever zone
data changes or when signatures expire, so performance
certainly is of a bigger concern. As for KSK, it is used less
frequently, so performance is less of a factor, but its impact is bigger
because of its role in signing other keys.
In earlier versions of this guide, the following key lengths were
chosen for each set, with the recommendation that they be rotated more
frequently for better security:
ZSK: RSA 1024 bits, rollover every year
KSK: RSA 2048 bits, rollover every five years
These should be considered minimum RSA key sizes. At the time
of this writing (mid-2020), the root zone and many TLDs are already using 2048
bit ZSKs. If you choose to implement larger key sizes, keep in mind that
larger key sizes result in larger DNS responses, which this may mean more
load on network resources. Depending on your network configuration, end users
may even experience resolution failures due to the increased response
sizes, as discussed in What’s EDNS All About (And Why Should I Care)?.
ECDSA key sizes can be much smaller for the same level of security, e.g.,
an ECDSA key length of 224 bits provides the same level of security as a
2048-bit RSA key. Currently BIND 9 sets a key size of 256 for all ECDSA keys.
The beauty of a public key cryptography system is that the public key
portion can and should be distributed to as many people as possible. As
the administrator, you may want to keep the public keys on an easily
accessible file system for operational ease, but there is no need to
securely store them, since both ZSK and KSK public keys are published in
the zone data as DNSKEY resource records.
Additionally, a hash of the KSK public key is also uploaded to the
parent zone (see Working With the Parent Zone for more details),
and is published by the parent zone as DS records.
Ideally, private keys should be stored offline, in secure devices such
as a smart card. Operationally, however, this creates certain
challenges, since the private key is needed to create RRSIG resource
records, and it is a hassle to bring the private key out of
storage every time the zone file changes or signatures expire.
A common approach to strike the balance between security and
practicality is to have two sets of keys: a ZSK set and a KSK set. A ZSK
private key is used to sign zone data, and can be kept online for ease
of use, while a KSK private key is used to sign just the DNSKEY (the ZSK); it is
used less frequently, and can be stored in a much more secure and
restricted fashion.
For example, a KSK private key stored on a USB flash drive that is kept
in a fireproof safe, only brought online once a year to sign a new pair
of ZSKs, combined with a ZSK private key stored on the network
file system and available for routine use, may be a good balance between
operational flexibility and security.
For more information on changing keys, please see
Key Rollovers.
A Hardware Security Module (HSM) may come in different shapes and sizes,
but as the name indicates, it is a physical device or devices, usually
with some or all of the following features:
Tamper-resistant key storage
Strong random-number generation
Hardware for faster cryptographic operations
Most organizations do not incorporate HSMs into their security practices
due to cost and the added operational complexity.
BIND supports Public Key Cryptography Standard #11 (PKCS #11) for
communication with HSMs and other cryptographic support devices. For
more information on how to configure BIND to work with an HSM, please
refer to the BIND 9 Administrator Reference
Manual.
A key rollover is where one key in a zone is replaced by a new one.
There are arguments for and against regularly rolling keys. In essence
these are:
Pros:
Regularly changing the key hinders attempts at determination of the
private part of the key by cryptanalysis of signatures.
It gives administrators practice at changing a key; should a key ever need to be
changed in an emergency, they would not be doing it for the first time.
Cons:
A lot of effort is required to hack a key, and there are probably
easier ways of obtaining it, e.g., by breaking into the systems on
which it is stored.
Rolling the key adds complexity to the system and introduces the
possibility of error. We are more likely to
have an interruption to our service than if we had not rolled it.
Whether and when to roll the key is up to you. How serious would the
damage be if a key were compromised without you knowing about it? How
serious would a key roll failure be?
Before going any further, it is worth noting that if you sign your zone
with either of the fully automatic methods (described in ref:signing_alternative_ways),
you don’t really need to
concern yourself with the details of a key rollover: BIND 9 takes care of
it all for you. If you are doing a manual key roll or are setting up the
keys for a semi-automatic key rollover, you do need to familiarize yourself
with the various steps involved and the timing details.
Rolling a key is not as simple as replacing the DNSKEY statement in the
zone. That is an essential part of it, but timing is everything. For
example, suppose that we run the example.com zone and that a friend
queries for the AAAA record of www.example.com. As part of the
resolution process (described in
How Does DNSSEC Change DNS Lookup?), their recursive server
looks up the keys for the example.com zone and uses them to verify
the signature associated with the AAAA record. We’ll assume that the
records validated successfully, so they can use the
address to visit example.com’s website.
Let’s also assume that immediately after the lookup, we want to roll the ZSK
for example.com. Our first attempt at this is to remove the old
DNSKEY record and signatures, add a new DNSKEY record, and re-sign the
zone with it. So one minute our server is serving the old DNSKEY and
records signed with the old key, and the next minute it is serving the
new key and records signed with it. We’ve achieved our goal - we are
serving a zone signed with the new keys; to check this is really the
case, we booted up our laptop and looked up the AAAA record
ftp.example.com. The lookup succeeded so all must be well. Or is it?
Just to be sure, we called our friend and asked them to check. They
tried to lookup ftp.example.com but got a SERVFAIL response from
their recursive server. What’s going on?
The answer, in a word, is “caching.” When our friend looked up
www.example.com, their recursive server retrieved and cached
not only the AAAA record, but also a lot of other records. It cached
the NS records for com and example.com, as well as
the AAAA (and A) records for those name servers (and this action may, in turn, have
caused the lookup and caching of other NS and AAAA/A records). Most
importantly for this example, it also looked up and cached the DNSKEY
records for the root, com, and example.com zones. When a query
was made for ftp.example.com, the recursive server believed it
already had most of the information
we needed. It knew what nameservers served example.com and their
addresses, so it went directly to one of those to get the AAAA record for
ftp.example.com and its associated signature. But when it tried to
validate the signature, it used the cached copy of the DNSKEY, and that
is when our friend had the problem. Their recursive server had a copy of
the old DNSKEY in its cache, but the AAAA record for ftp.example.com
was signed with the new key. So, not surprisingly, the signature could not
validate.
How should we roll the keys for example.com? A clue to the
answer is to note that the problem came about because the DNSKEY records
were cached by the recursive server. What would have happened had our
friend flushed the DNSKEY records from the recursive server’s cache before
making the query? That would have worked; those records would have been
retrieved from example.com’s nameservers at the same time that we
retrieved the AAAA record for ftp.example.com. Our friend’s server would have
obtained the new key along with the AAAA record and associated signature
created with the new key, and all would have been well.
As it is obviously impossible for us to notify all recursive server
operators to flush our DNSKEY records every time we roll a key, we must
use another solution. That solution is to wait
for the recursive servers to remove old records from caches when they
reach their TTL. How exactly we do this depends on whether we are trying
to roll a ZSK, a KSK, or a CSK.
The ZSK can be rolled in one of the following two ways:
Pre-Publication: Publish the new ZSK into zone data before it is
actually used. Wait at least one TTL interval, so the world’s recursive servers
know about both keys, then stop using the old key and generate a new
RRSIG using the new key. Wait at least another TTL, so the cached old
key data is expunged from the world’s recursive servers, and then remove
the old key.
The benefit of the pre-publication approach is it does not
dramatically increase the zone size; however, the duration of the rollover
is longer. If insufficient time has passed after the new ZSK is
published, some resolvers may only have the old ZSK cached when the
new RRSIG records are published, and validation may fail. This is the
method described in ZSK Rollover.
Double-Signature: Publish the new ZSK and new RRSIG, essentially
doubling the size of the zone. Wait at least one TTL interval, and then remove
the old ZSK and old RRSIG.
The benefit of the double-signature approach is that it is easier to
understand and execute, but it causes a significantly increased zone size
during a rollover event.
Rolling the KSK requires interaction with the parent zone, so
operationally this may be more complex than rolling ZSKs. There are
three methods of rolling the KSK:
Double-KSK: Add the new KSK to the DNSKEY RRset, which is then
signed with both the old and new keys. After waiting for the old RRset
to expire from caches, change the DS record in the parent zone.
After waiting a further TTL interval for this change to be reflected in
caches, remove the old key from the RRset.
Basically, the new KSK is added first at the child zone and
used to sign the DNSKEY; then the DS record is changed, followed by the
removal of the old KSK. Double-KSK keeps the interaction with the
parent zone to a minimum, but for the duration of the rollover, the
size of the DNSKEY RRset is increased.
Double-DS: Publish the new DS record. After waiting for this
change to propagate into caches, change the KSK. After a further TTL
interval during which the old DNSKEY RRset expires from caches, remove the
old DS record.
Double-DS is the reverse of Double-KSK: the new DS is published at
the parent first, then the KSK at the child is updated, then
the old DS at the parent is removed. The benefit is that the size of the DNSKEY
RRset is kept to a minimum, but interactions with the parent zone are
increased to two events. This is the method described in
KSK Rollover.
Double-RRset: Add the new KSK to the DNSKEY RRset, which is
then signed with both the old and new key, and add the new DS record
to the parent zone. After waiting a suitable interval for the
old DS and DNSKEY RRsets to expire from caches, remove the old DNSKEY and
old DS record.
Double-RRset is the fastest way to roll the KSK (i.e., it has the shortest rollover
time), but has the drawbacks of both of the other methods: a larger
DNSKEY RRset and two interactions with the parent.
Rolling the CSK is more complex than rolling either the ZSK or KSK, as
the timing constraints relating to both the parent zone and the caching
of records by downstream recursive servers must be taken into
account. There are numerous possible methods that are a combination of ZSK
rollover and KSK rollover methods. BIND 9 automatic signing uses a
combination of ZSK Pre-Publication and Double-KSK rollover.
Keys are generally rolled on a regular schedule - if you choose
to roll them at all. But sometimes, you may have to rollover keys
out-of-schedule due to a security incident. The aim of an emergency
rollover is to re-sign the zone with a new key as soon as possible, because
when a key is suspected of being compromised, a malicious attacker (or
anyone who has access to the key) could impersonate your server and trick other
validating resolvers into believing that they are receiving authentic,
validated answers.
During an emergency rollover, follow the same operational
procedures described in Rollovers, with the added
task of reducing the TTL of the current active (potentially compromised) DNSKEY
RRset, in an attempt to phase out the compromised key faster before the new
key takes effect. The time frame should be significantly reduced from
the 30-days-apart example, since you probably do not want to wait up to
60 days for the compromised key to be removed from your zone.
Another method is to carry a spare key with you at all times. If
you have a second key pre-published and that one
is not compromised at the same time as the first key,
you could save yourself some time by immediately
activating the spare key if the active
key is compromised. With pre-publication, all validating resolvers should already
have this spare key cached, thus saving you some time.
With a KSK emergency rollover, you also need to consider factors
related to your parent zone, such as how quickly they can remove the old
DS records and publish the new ones.
As with many other facets of DNSSEC, there are multiple aspects to take into
account when it comes to emergency key rollovers. For more in-depth
considerations, please check out RFC 7583.
From time to time, new digital signature algorithms with improved
security are introduced, and it may be desirable for administrators to
roll over DNSKEYs to a new algorithm, e.g., from RSASHA1 (algorithm 5 or
7) to RSASHA256 (algorithm 8). The algorithm rollover steps must be followed with
care to avoid breaking DNSSEC validation.
If you are managing DNSSEC by using the dnssec-policy configuration,
named handles the rollover for you. Simply change the algorithm
for the relevant keys, and named uses the new algorithm when the
key is next rolled. It performs a smooth transition to the new
algorithm, ensuring that the zone remains valid throughout rollover.
If you are using other methods to sign the zone, the administrator needs to do more work. As
with other key rollovers, when the zone is a primary zone, an algorithm
rollover can be accomplished using dynamic updates or automatic key
rollovers. For secondary zones, only automatic key rollovers are
possible, but the dnssec-settime utility can be used to control the
timing.
In any case, the first step is to put DNSKEYs in place using the new algorithm.
You must generate the K* files for the new algorithm and put
them in the zone’s key directory, where named can access them. Take
care to set appropriate ownership and permissions on the keys. If the
auto-dnssec zone option is set to maintain, named
automatically signs the zone with the new keys, based on their timing
metadata when the dnssec-loadkeys-interval elapses or when you issue the
rndcloadkeys command. Otherwise, for primary zones, you can use
nsupdate to add the new DNSKEYs to the zone; this causes named
to use them to sign the zone. For secondary zones, e.g., on a
“bump in the wire” signing server, nsupdate cannot be used.
Once the zone has been signed by the new DNSKEYs (and you have waited
for at least one TTL period), you must inform the parent zone and any trust
anchor repositories of the new KSKs, e.g., you might place DS records in
the parent zone through your DNS registrar’s website.
Before starting to remove the old algorithm from a zone, you must allow
the maximum TTL on its DS records in the parent zone to expire. This
assures that any subsequent queries retrieve the new DS records
for the new algorithm. After the TTL has expired, you can remove the DS
records for the old algorithm from the parent zone and any trust anchor
repositories. You must then allow another maximum TTL interval to elapse
so that the old DS records disappear from all resolver caches.
The next step is to remove the DNSKEYs using the old algorithm from your
zone. Again this can be accomplished using nsupdate to delete the
old DNSKEYs (for primary zones only) or by automatic key rollover when
auto-dnssec is set to maintain. You can cause the automatic key
rollover to take place immediately by using the dnssec-settime
utility to set the Delete date on all keys to any time in the past.
(See the dnssec-settime-D<date/offset> option.)
After adjusting the timing metadata, the rndcloadkeys command
causes named to remove the DNSKEYs and
RRSIGs for the old algorithm from the zone. Note also that with the
nsupdate method, removing the DNSKEYs also causes named to
remove the associated RRSIGs automatically.
Once you have verified that the old DNSKEYs and RRSIGs have been removed
from the zone, the final (optional) step is to remove the key files for
the old algorithm from the key directory.
Dynamic DNS (DDNS) is actually independent of DNSSEC. DDNS provides a
mechanism, separate from editing the zone file or zone database, to edit DNS
data. Most DNS clients and servers are able to handle dynamic
updates, and DDNS can also be integrated as part of your DHCP
environment.
When you have both DNSSEC and dynamic updates in your environment,
updating zone data works the same way as with traditional (insecure)
DNS: you can use rndcfreeze before editing the zone file, and
rndcthaw when you have finished editing, or you can use the
command nsupdate to add, edit, or remove records like this:
$ nsupdate
> server 192.168.1.13
> update add xyz.example.com. 300 IN A 1.1.1.1
> send
> quit
The examples provided in this guide make named automatically
re-sign the zone whenever its content has changed. If you decide to sign
your own zone file manually, you need to remember to execute the
dnssec-signzone command whenever your zone file has been updated.
As far as system resources and performance are concerned, be mindful that
with a DNSSEC zone that changes frequently, every time the zone
changes your system is executing a series of cryptographic operations
to (re)generate signatures and NSEC or NSEC3 records.
Let’s clarify what we mean: in this section, “private networks” really refers to
a private or internal DNS view. Most DNS products offer the ability to
have different versions of DNS answers, depending on the origin of the
query. This feature is often called “DNS views” or “split DNS,” and is most
commonly implemented as an “internal” versus an “external” setup.
For instance, your organization may have a version of example.com
that is offered to the world, and its names most likely resolve to
publicly reachable IP addresses. You may also have an internal version
of example.com that is only accessible when you are on the company’s
private networks or via a VPN connection. These private networks typically
fall under 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 for IPv4.
So what if you want to offer DNSSEC for your internal version of
example.com? This can be done: the golden rule is to use the same
key for both the internal and external versions of the zones. This
avoids problems that can occur when machines (e.g., laptops) move
between accessing the internal and external zones, when it is possible
that they may have cached records from the wrong zone.
With your DNS infrastructure secured with DNSSEC, information can
now be stored in DNS and its integrity and authenticity can be proved.
One of the new features that takes advantage of this is the DNS-Based
Authentication of Named Entities, or DANE. This improves security in a
number of ways, including:
The ability to store self-signed X.509 certificates and bypass having to pay a third
party (such as a Certificate Authority) to sign the certificates
(RFC 6698).
Improved security for clients connecting to mail servers (RFC 7672).
A secure way of getting public PGP keys (RFC 7929).
DNSSEC, like many things in this world, is not without its problems.
Below are a few challenges and disadvantages that DNSSEC faces.
Increased, well, everything: With DNSSEC, signed zones are larger,
thus taking up more disk space; for DNSSEC-aware servers, the
additional cryptographic computation usually results in increased
system load; and the network packets are bigger, possibly putting
more strains on the network infrastructure.
Different security considerations: DNSSEC addresses many security
concerns, most notably cache poisoning. But at the same time, it may
introduce a set of different security considerations, such as
amplification attack and zone enumeration through NSEC. These
concerns are still being identified and addressed by the Internet
community.
More complexity: If you have read this far, you have probably already
concluded this yourself. With additional resource records, keys,
signatures, and rotations, DNSSEC adds many more moving pieces on top of
the existing DNS machine. The job of the DNS administrator changes,
as DNS becomes the new secure repository of everything from spam
avoidance to encryption keys, and the amount of work involved to
troubleshoot a DNS-related issue becomes more challenging.
Increased fragility: The increased complexity means more
opportunities for things to go wrong. Before DNSSEC, DNS
was essentially “add something to the zone and forget it.” With DNSSEC,
each new component - re-signing, key rollover, interaction with
parent zone, key management - adds more opportunity for error. It is
entirely possible that a failure to validate a name may come down to
errors on the part of one or more zone operators rather than the
result of a deliberate attack on the DNS.
New maintenance tasks: Even if your new secure DNS infrastructure
runs without any hiccups or security breaches, it still requires
regular attention, from re-signing to key rollovers. While most of
these can be automated, some of the tasks, such as KSK rollover,
remain manual for the time being.
Not enough people are using it today: While it’s estimated (as of
mid-2020) that roughly 30% of the global Internet DNS traffic is
validating 9 , that doesn’t mean that many of the DNS zones are
actually signed. What this means is, even if your company’s zone is
signed today, fewer than 30% of the Internet’s servers are taking
advantage of this extra security. It gets worse: with less than 1.5%
of the com. domains signed, even if your DNSSEC validation is enabled today,
it’s not likely to buy you or your users a whole lot more protection
until these popular domain names decide to sign their zones.
The last point may have more impact than you realize. Consider this:
HTTP and HTTPS make up the majority of traffic on the Internet. While you may have
secured your DNS infrastructure through DNSSEC, if your web hosting is
outsourced to a third party that does not yet support DNSSEC in its
own domain, or if your web page loads contents and components from
insecure domains, end users may experience validation problems when
trying to access your web page. For example, although you may have signed
the zone company.com, the web address www.company.com may actually be a
CNAME to foo.random-cloud-provider.com. As long as
random-cloud-provider.com remains an insecure DNS zone, users cannot
fully validate everything when they visit your web page and could be
redirected elsewhere by a cache poisoning attack.
There are two recipes here: the first shows an example using DNSSEC
signing on the primary server, which has been covered in this
guide; the second shows how to setup a “bump in the
wire” between a hidden primary and the secondary servers to seamlessly
sign the zone “on the fly.”
In this recipe, our servers are illustrated as shown in
DNSSEC Signing Recipe #1: we have a primary server
(192.168.1.1) and three secondary servers (192.168.1.2, 192.168.1.3, and
192.168.1.4) that receive zone transfers. To get the zone
signed, we need to reconfigure the primary server. Once reconfigured, a
signed version of the zone is generated on the fly;
zone transfers take care of synchronizing the signed zone data
to all secondary name servers, without configuration or software changes
on them.
Using the method described in
Easy-Start Guide for Signing Authoritative Zones, we just need to
add a dnssec-policy statement to the relevant zone clause. This is
what the named.conf zone statement looks like on the primary server, 192.168.1.1:
We have chosen to use the default policy, storing the keys generated for
the zone in the directory keys/example.com. To use a
custom policy, define the policy in the configuration
file and select it in the zone statement (as described in
Creating a Custom DNSSEC Policy).
On the secondary servers, named.conf does not need to be updated,
and it looks like this:
In this recipe, we take advantage of the power of automated signing
by placing an additional name server (192.168.1.5) between the hidden
primary (192.168.1.1) and the DNS secondaries (192.168.1.2, 192.168.1.3,
and 192.168.1.4). The additional name server, 192.168.1.5, acts as a “bump
in the wire,” taking an unsigned zone from the hidden primary,
and sending out signed data on the other end to the secondary name
servers. The steps described in this recipe may be used as part of a
DNSSEC deployment strategy, since it requires only minimal changes made to
the existing hidden DNS primary and DNS secondaries.
It is important to remember that 192.168.1.1 in this case is a hidden
primary not exposed to the world, and it must not be listed in the NS RRset.
Otherwise the world will get conflicting answers: unsigned answers from
the hidden primary and signed answers from the other name servers.
The only configuration change needed on the hidden primary, 192.168.1.1,
is to make sure it allows our middle box to perform a zone transfer:
On the middle box, 192.168.1.5, all the tasks described in
Easy-Start Guide for Signing Authoritative Zones still need to be
performed, such as generating key pairs and uploading information to
the parent zone. This server is configured as secondary to the hidden
primary 192.168.1.1 to receive the unsigned data; then, using keys
accessible to this middle box, to sign data on the fly; and finally, to send out the
signed data via zone transfer to the other three DNS secondaries. Its
named.conf zone statement looks like this:
(As before, the default policy has been selected here. See
Creating a Custom DNSSEC Policy for instructions on how to define
and use a custom policy.)
Finally, on the three secondary servers, the configuration should be updated
to receive a zone transfer from 192.168.1.5 (the middle box) instead of
from 192.168.1.1 (the hidden primary). If using BIND, the named.conf file looks
like this:
zone"example.com"IN{typesecondary;file"db/example.com.db";primaries{192.168.1.5;};# this was 192.168.1.1 before!};
If you are signing your zone using a dnssec-policy statement, this
section is not really relevant to you. In the policy statement, you set how long
you want your keys to be valid for, the time
taken for information to propagate through your zone, the time it takes
for your parent zone to register a new DS record, etc., and that’s more
or less it. named implements everything for you automatically, apart from
uploading the new DS records to your parent zone - which is covered in
Uploading Information to the Parent Zone. (Some
screenshots from a session where a KSK is uploaded to the parent zone
are presented here for convenience.) However, these recipes may be useful
in describing what happens
through the rollover process and what you should be monitoring.
This recipe covers how to perform a ZSK rollover using what is known as
the Pre-Publication method. For other ZSK rolling methods, please see
ZSK Rollover Methods in Advanced Discussions.
Below is a sample timeline for a ZSK rollover to occur on January 1, 2021:
December 1, 2020 (one month before rollover)
Generate new ZSK
Add DNSKEY for new ZSK to zone
January 1, 2021 (day of rollover)
New ZSK used to replace RRSIGs for the bulk of the zone
February 1, 2021 (one month after rollover)
Remove old ZSK DNSKEY RRset from zone
DNSKEY signatures made with KSK are changed
The current active ZSK has the ID 17694 in the example below. For more
information on key management and rollovers, please see
Rollovers.
On December 1, 2020, a month before the example rollover, you (as administrator)
should change the parameters on the current key (17694). Set it to become inactive on
January 1, 2021 and be deleted from the zone on February 1, 2021; also,
generate a successor key (51623):
The first command gets us into the key directory
/etc/bind/keys/example.com/, where keys for example.com are
stored.
The second, dnssec-settime, sets an inactive (-I) date of January 1,
2021, and a deletion (-D) date of February 1, 2021, for the current ZSK
(Kexample.com.+008+17694).
The third command, dnssec-keygen, creates a successor key, using
the exact same parameters (algorithms, key sizes, etc.) as the current
ZSK. The new ZSK created in our example is Kexample.com.+008+51623.
Make sure the successor keys are readable by named.
named’s logging messages indicate when the next
key checking event is scheduled to occur, the frequency of which can be
controlled by dnssec-loadkeys-interval. The log message looks like
this:
And you can check the publish date of the key by looking at the key
file:
# cd /etc/bind/keys/example.com# cat Kexample.com.+008+51623.key;Thisisazone-signingkey,keyid11623,forexample.com.;Created:20201130160024(MonDec100:00:242020);Publish:20201202000000(FriDec208:00:002020);Activate:20210101000000(SunJan108:00:002021)...
Since the publish date is set to the morning of December 2, and our example
scenario takes place on December 1, the next
morning you will notice that your zone has gained a new DNSKEY record,
but the new ZSK is not yet being used to generate signatures. Below is
the abbreviated output - with shortened DNSKEY and RRSIG - when querying the
authoritative name server, 192.168.1.13:
For good measure, let’s take a look at the SOA record and its
signature for this zone. Notice the RRSIG is signed by the current ZSK,
17694. This will come in handy later when you want to verify whether
the new ZSK is in effect:
$ dig @192.168.1.13 example.com. SOA +dnssec +multiline
...
;; ANSWER SECTION:
example.com. 600 IN SOA ns1.example.com. admin.example.com. (
2020120102 ; serial
1800 ; refresh (30 minutes)
900 ; retry (15 minutes)
2419200 ; expire (4 weeks)
300 ; minimum (5 minutes)
)
example.com. 600 IN RRSIG SOA 8 2 600 (
20201230160109 20201130150109 17694 example.com.
YUTC8rFULaWbW+nAHzbfGwNqzARHevpryzRIJMvZBYPo
NAeejNk9saNAoCYKWxGJ0YBc2k+r5fYq1Mg4ll2JkBF5
buAsAYLw8vEOIxVpXwlArY+oSp9T1w2wfTZ0vhVIxaYX
6dkcz4I3wbDx2xmG0yngtA6A8lAchERx2EGy0RM= )
These are all the manual tasks you need to perform for a ZSK rollover.
If you have followed the configuration examples in this guide of using
inline-signing and auto-dnssec, everything else is automated for
you by BIND.
On the actual day of the rollover, although there is technically nothing
for you to do, you should still keep an eye on the zone to make sure new
signatures are being generated by the new ZSK (51623 in this example).
The easiest way is to query the authoritative name server 192.168.1.13
for the SOA record as you did a month ago:
As you can see, the signature generated by the old ZSK (17694) has
disappeared, replaced by a new signature generated from the new ZSK
(51623).
Note
Not all signatures will disappear magically on the same day;
it depends on when each one was generated. In the worst-case scenario,
a new signature could have been signed by the old ZSK (17694) moments
before it was deactivated, meaning that the signature could live for almost
30 more days, until just before February 1.
This is why it is important to keep the old ZSK in the
zone and not delete it right away.
Again, technically there is nothing you need to do on this day,
but it doesn’t hurt to verify that the old ZSK (17694) is now completely
gone from your zone. named will not touch
Kexample.com.+008+17694.private and Kexample.com.+008+17694.key
on your file system. Running the same dig command for DNSKEY should
suffice:
Congratulations, the ZSK rollover is complete! As for the actual key
files (the files ending in .key and .private), they may be deleted at this
point, but they do not have to be.
This recipe describes how to perform KSK rollover using the Double-DS
method. For other KSK rolling methods, please see
KSK Rollover Methods in
Advanced Discussions. The registrar used in this
recipe is GoDaddy. Also for this recipe,
we are keeping the number of DS records down to just one per active set
using just SHA-1, for the sake of better clarity, although in practice
most zone operators choose to upload two DS records as shown in
Working With the Parent Zone. For more information on key
management and rollovers,
please see Rollovers.
Below is a sample timeline for a KSK rollover to occur on January 1, 2021:
December 1, 2020 (one month before rollover)
Change timer on the current KSK
Generate new KSK and DS records
Add DNSKEY for the new KSK to zone
Upload new DS records to parent zone
January 1, 2021 (day of rollover)
Use the new KSK to sign all DNSKEY RRsets, which generates new
RRSIGs
Add new RRSIGs to the zone
Remove RRSIG for the old ZSK from zone
Start using the new KSK to sign DNSKEY
February 1, 2021 (one month after rollover)
Remove the old KSK DNSKEY from zone
Remove old DS records from parent zone
The current active KSK has the ID 24828, and this is the DS record that
has already been published by the parent zone:
# dnssec-dsfromkey -a SHA-1 Kexample.com.+007+24828.keyexample.com.INDS2482871D4A33E8DD550A9567B4C4971A34AD6C4B80A6AD3
On December 1, 2020, a month before the planned rollover, you (as
administrator) should
change the parameters on the current key. Set it to become inactive on January
1, 2021, and be deleted from the zone on February 1st, 2021;
also generate a successor key (23550). Finally, generate a new
DS record based on the new key, 23550:
# cd /etc/bind/keys/example.com/# dnssec-settime -I 20210101 -D 20210201 Kexample.com.+007+24828./Kexample.com.+007+24848.key./Kexample.com.+007+24848.private# dnssec-keygen -S Kexample.com.+007+24848Generatingkeypair.......................................................................................++...................................++Kexample.com.+007+23550# dnssec-dsfromkey -a SHA-1 Kexample.com.+007+23550.keyexample.com.INDS235507154FCF030AA1C79C0088FDEC1BD1C37DAA2E70DFB
The first command gets us into the key directory
/etc/bind/keys/example.com/, where keys for example.com are
stored.
The second, dnssec-settime, sets an inactive (-I) date of January 1,
2021, and a deletion (-D) date of February 1, 2021 for the current KSK
(Kexample.com.+007+24848).
The third command, dnssec-keygen, creates a successor key, using
the exact same parameters (algorithms, key sizes, etc.) as the current
KSK. The new key pair created in our example is Kexample.com.+007+23550.
The fourth and final command, dnssec-dsfromkey, creates a DS record
from the new KSK (23550), using SHA-1 as the digest type. Again, in
practice most people generate two DS records for both supported digest
types (SHA-1 and SHA-256), but for our example here we are only using
one to keep the output small and hopefully clearer.
Make sure the successor keys are readable by named.
The syslog message indicates when the next key
checking event is. The log message looks like this:
You can check the publish date of the key by looking at the key
file:
# cd /etc/bind/keys/example.com# cat Kexample.com.+007+23550.key;Thisisakey-signingkey,keyid23550,forexample.com.;Created:20201130160024(ThuDec100:00:242020);Publish:20201202000000(FriDec208:00:002020);Activate:20210101000000(SunJan108:00:002021)...
Since the publish date is set to the morning of December 2, and our example
scenario takes place on December 1, the next
morning you will notice that your zone has gained a new DNSKEY record
based on your new KSK, but with no corresponding RRSIG yet. Below is the
abbreviated output - with shortened DNSKEY and RRSIG - when querying the
authoritative name server, 192.168.1.13:
Anytime after generating the DS record, you can upload it;
it is not necessary to wait for the DNSKEY to be published in your zone,
since this new KSK is not active yet. You can do it
immediately after the new DS record has been generated on December 1,
or you can wait until the next day after you have verified that the
new DNSKEY record is added to the zone. Below are some screenshots from
GoDaddy’s web-based interface, used to add a new DS record 10.
After logging in, click the green “Launch” button next to the domain
name you want to manage.
Finally, let’s verify that the registrar has published the new DS
record. This may take anywhere from a few minutes to a few days,
depending on your parent zone. You can verify whether your
parent zone has published the new DS record by querying for the DS
record of your zone. In the example below, the Google public DNS server
8.8.8.8 is used:
You can also query your parent zone’s authoritative name servers
directly to see if these records have been published. DS records will
not show up on your own authoritative zone, so you cannot query your own
name servers for them. In this recipe, the parent zone is .com, so
querying a few of the .com name servers is another appropriate
verification.
If you have followed the examples in this document, as described in
Easy-Start Guide for Signing Authoritative Zones, there is
technically nothing you need to do manually on the actual day of the
rollover. However, you should still keep an eye on the zone to make sure
new signature(s) are being generated by the new KSK (23550 in this
example). The easiest way is to query the authoritative name server
192.168.1.13 for the same DNSKEY and signatures, as you did a month
ago:
While the removal of the old DNSKEY from the zone should be automated by
named, the removal of the DS record is manual. You should make sure
the old DNSKEY record is gone from your zone first, by querying for the
DNSKEY records of the zone; this time we expect not to see
the key with an ID of 24828:
Since the key with the ID 24828 is gone, you can now remove the old DS
record for that key from our parent zone.
Be careful to remove the correct DS record. If you accidentally remove
the new DS record(s) with key ID 23550, it could lead to a problem called
“security lameness,” as discussed in
Security Lameness, and may cause users to be unable
to resolve any names in the zone.
After logging in (again, GoDaddy.com in our example) and launching the domain, scroll down to the “DS
Records” section and click Manage.
Congratulations, the KSK rollover is complete! As for the actual key
files (ending in .key and .private), they may be deleted at this
point, but they do not have to be.
The screenshots were taken from GoDaddy’s interface at the time the
original version of this guide was published (2015). It may have
changed since then.
If your zone is signed with RSASHA1 (algorithm 5), you cannot migrate
to NSEC3 without also performing an
algorithm rollover
to RSASHA1-NSEC3-SHA1 (algorithm 7), as described in
Algorithm Rollovers. This
ensures that older validating resolvers that do not understand
NSEC3 will fall back to treating the zone as unsecured (rather than
“bogus”), as described in Section 2 of RFC 5155.
To enable NSEC3, update your dnssec-policy and add the desired NSEC3
parameters. The example below enables NSEC3 for zones with the standard
DNSSEC policy, using 0 additional iterations, no opt-out, and a zero-length salt:
You can also verify that it worked by querying for a name that you know
does not exist, and checking for the presence of the NSEC3 record.
For example:
$ dig @192.168.1.13 thereisnowaythisexists.example.com. A +dnssec +multiline
...
5A03TL362CS8VSIH69CVA4MJIKRHFQH3.example.com. 300 IN NSEC3 1 0 0 - (
TQ9QBEGA6CROHEOC8KIH1A2C06IVQ5ER
NS SOA RRSIG DNSKEY NSEC3PARAM )
...
Our example used four parameters: 1, 0, 0, and -, in
order. 1 represents the algorithm, 0 represents the
opt-out flag, 0 represents the number of additional iterations, and
- denotes no salt is used. To learn more about each of these
parameters, please see NSEC3PARAM.
Migrating from NSEC3 back to NSEC is easy; just remove the nsec3param
configuration option from your dnssec-policy and reconfigure the name
server. You can tell that it worked if you see these messages in the log:
This recipe discusses how to enable and disable NSEC3 opt-out, and how to show
the results of each action. As discussed in
NSEC3 Opt-Out, NSEC3 opt-out is a feature
that can help conserve resources on parent zones with many
delegations that have not yet been signed.
Warning
NSEC3 Opt-Out feature brings benefit only to _extremely_ large zones with lots
of insecure delegations. It’s use is counterproductive in all other cases as
it decreases tamper-resistance of the zone and also decreases efficiency of
resolver cache (see RFC 8198).
In other words, don’t enable Opt-Out unless you are serving an equivalent of
com. zone.
Because the NSEC3PARAM record does not keep track of whether opt-out is used,
it is hard to check whether changes need to be made to the NSEC3 chain if the flag
is changed. Similar to changing the NSEC3 salt, your best option is to change
the value of optout together with another NSEC3 parameter, like
iterations, and in a following step restore the iterations value.
For this recipe we assume the zone example.com
has the following four entries (for this example, it is not relevant what
record types these entries are):
ns1.example.com
ftp.example.com
www.example.com
web.example.com
And the zone example.com has five delegations to five subdomains, only one of
which is signed and has a valid DS RRset:
aaa.example.com, not signed
bbb.example.com, signed
ccc.example.com, not signed
ddd.example.com, not signed
eee.example.com, not signed
Before enabling NSEC3 opt-out, the zone example.com contains ten
NSEC3 records; below is the list with the plain text name before the actual
NSEC3 record:
After NSEC3 opt-out is enabled, the number of NSEC3 records is reduced.
Notice that the unsigned delegations aaa, ccc, ddd, and
eee no longer have corresponding NSEC3 records.
NSEC3 hashes the plain text domain name, and we can compute our own
hashes using the tool nsec3hash. For example, to compute the
hashed name for www.example.com using the parameters we listed
above, we can execute this command:
This recipe describes how to revert from a signed zone (DNSSEC) back to
an unsigned (DNS) zone.
Here is what named.conf looks like when it is signed:
zone "example.com" IN {
type primary;
file "db/example.com.db";
dnssec-policy "default";
inline-signing yes;
};
To indicate the reversion to unsigned, change the dnssec-policy line:
zone "example.com" IN {
type primary;
file "db/example.com.db";
dnssec-policy "insecure";
inline-signing yes;
};
Then use rndcreload to reload the zone.
The “insecure” policy is a built-in policy (like “default”). It makes sure
the zone is still DNSSEC-maintained, to allow for a graceful transition to
unsigned. It also publishes the CDS and CDNSKEY DELETE records automatically
at the appropriate time.
If the parent zone allows management of DS records via CDS/CDNSKEY, as described in
RFC 8078, the DS record should be removed from the parent automatically.
Otherwise, DS records can be removed via the registrar. Below is an example
showing how to remove DS records using the
GoDaddy web-based interface:
After logging in, click the green “Launch” button next to the domain
name you want to manage.
When the DS records have been removed from the parent zone, use
rndcdnssec-checkds-key<id>withdrawnexample.com to tell named that
the DS is removed, and the remaining DNSSEC records will be removed in a timely
manner. Or, if parental agents are configured, the DNSSEC records will be
automatically removed after BIND has seen that the parental agents no longer
serve the DS RRset for this zone.
After a while, the zone is reverted back to the traditional, insecure DNS
format. This can be verified by checking that all DNSKEY and RRSIG records have been
removed from the zone.
The dnssec-policy line can then be removed from named.conf and
the zone reloaded. The zone will no longer be subject to any DNSSEC
maintenance.
Below are some common questions and (hopefully) some answers that
help.
Do I need IPv6 to have DNSSEC?
No. DNSSEC can be deployed without IPv6.
Does DNSSEC encrypt my DNS traffic, so others cannot eavesdrop on my DNS queries?
No. Although cryptographic keys and digital signatures
are used in DNSSEC, they only provide authenticity and integrity, not
privacy. Someone who sniffs network traffic can still see all the DNS
queries and answers in plain text; DNSSEC just makes it very difficult
for the eavesdropper to alter or spoof the DNS responses.
For protection against eavesdropping, the preferred protocol is DNS-over-TLS.
DNS-over-HTTPS can also do the job, but it is more complex.
If I deploy DNS-over-TLS/HTTPS, can I skip deploying DNSSEC?
No. DNS-over-encrypted-transport stops eavesdroppers on a network, but it does
not protect against cache poisoning and answer manipulation in other parts
of the DNS resolution chain. In other words, these technologies offer protection
only for records when they are in transit between two machines; any
compromised server can still redirect traffic elsewhere (or simply eavesdrop).
However, DNSSEC provides integrity and authenticity for DNS
records, even when these records are stored in caches and on disks.
Does DNSSEC protect the communication between my laptop and my name server?
Unfortunately, not at the moment. DNSSEC is designed to protect the
communication between end clients (laptop) and name servers;
however, there are few applications or stub resolver libraries as of
mid-2020 that take advantage of this capability.
Does DNSSEC secure zone transfers?
No. You should consider using TSIG to secure zone transfers among your
name servers.
Does DNSSEC protect my network from malicious websites?
DNSSEC makes it much more difficult for attackers to spoof DNS responses
or perform cache poisoning. It cannot protect against users who
visit a malicious website that an attacker owns and operates, or prevent users from
mistyping a domain name; it will just become less likely that an attacker can
hijack other domain names.
In other words, DNSSEC is designed to provide confidence that when
a DNS response is received for www.company.com over port 53, it really came from
Company’s name servers and the answers are authentic. But that does not mean
the web server a user visits over port 80 or port 443 is necessarily safe.
If I enable DNSSEC validation, will it break DNS lookup, since most domain names do not yet use DNSSEC?
No, DNSSEC is backwards-compatible to “standard” DNS. A DNSSEC-enabled
validating resolver can still look up all of these domain names as it always
has under standard DNS.
There are four (4) categories of responses (see RFC 4035):
Domains for which it is not possible to determine whether these domains use DNSSEC.
A DNSSEC-enabled validating resolver still resolves Secure and
Insecure; only Bogus and Indeterminate result in a
SERVFAIL.
As of mid-2022, roughly one-third of users worldwide are using DNSSEC validation
on their recursive name servers. Google public DNS (8.8.8.8) also has
enabled DNSSEC validation.
Do I need to have special client software to use DNSSEC?
No. DNSSEC only changes the communication
behavior among DNS servers, not between a DNS server (validating resolver) and
a client (stub resolver). With DNSSEC validation enabled on your recursive
server, if a domain name does not pass the checks, an error message
(typically SERVFAIL) is returned to clients; to most client
software today, it appears that the DNS query has failed or that the domain
name does not exist.
Since DNSSEC uses public key cryptography, do I need Public Key Infrastructure (PKI) in order to use DNSSEC?
No, DNSSEC does not depend on an existing PKI. Public keys are stored within
the DNS hierarchy; the trustworthiness of each zone is guaranteed by
its parent zone, all the way back to the root zone. A copy of the trust
anchor for the root zone is distributed with BIND 9.
Do I need to purchase SSL certificates from a Certificate Authority (CA) to use DNSSEC?
No. With DNSSEC, you generate and publish your own keys, and sign your own
data as well. There is no need to pay someone else to do it for you.
My parent zone does not support DNSSEC; can I still sign my zone?
Technically, yes, but you will not get
the full benefit of DNSSEC, as other validating resolvers are not
able to validate your zone data. Without the DS record(s) in your parent
zone, other validating resolvers treat your zone as an insecure
(traditional) zone, and no actual verification is carried out.
To the rest of the world, your zone still appears to be
insecure, and it will continue to be insecure until your parent zone can
host the DS record(s) for you and tell the rest of the world
that your zone is signed.
Is DNSSEC the same thing as TSIG?
No. TSIG is typically used
between primary and secondary name servers to secure zone transfers,
while DNSSEC secures DNS lookup by validating answers. Even if you enable
DNSSEC, zone transfers are still not validated; to
secure the communication between your primary and secondary name
servers, consider setting up TSIG or similar secure channels.
How are keys copied from primary to secondary server(s)?
DNSSEC uses public cryptography, which results in two types of keys: public and
private. The public keys are part of the zone data, stored as DNSKEY
record types. Thus the public keys are synchronized from primary to
secondary server(s) as part of the zone transfer. The private keys are
not, and should not be, stored anywhere other than secured on the primary server.
See Key Storage for
more information on key storage options and considerations.
Can I use the same key for multiple zones?
Yes and no. Good security practice
suggests that you should use unique key pairs for each zone, just as
you should have different passwords for your email account, social
media login, and online banking credentials. On a technical level, it
is completely feasible to reuse a key, but multiple zones are at risk if one key
pair is compromised. However, if you have hundreds or thousands
of zones to administer, a single key pair for all might be
less error-prone to manage. You may choose to use the same approach as
with password management: use unique passwords for your bank accounts and
shopping sites, but use a standard password for your not-very-important
logins. First, categorize your zones: high-value zones (or zones that have
specific key rollover requirements) get their own key pairs, while other,
more “generic” zones can use a single key pair for easier management. Note that
at present (mid-2020), fully automatic signing (using the dnssec-policy
clause in your named configuration file) does not support reuse of keys
except when the same zone appears in multiple views (see next question).
To use the same key for multiple zones, sign your
zones using semi-automatic signing. Each zone wishing to use the key
should point to the same key directory.
How do I sign the different instances of a zone that appears in multiple views?
Add a dnssec-policy statement to each zone definition in the
configuration file. To avoid problems when a single computer accesses
different instances of the zone while information is still in its cache
(e.g., a laptop moving from your office to a customer site), you
should sign all instances with the same key. This means setting the
same DNSSEC policy for all instances of the zone, and making sure that the
key directory is the same for all instances of the zone.
Will there be any problems if I change the DNSSEC policy for a zone?
If you are using fully automatic signing, no. Just change the parameters in the
dnssec-policy statement and reload the configuration file. named
makes a smooth transition to the new policy, ensuring that your zone
remains valid at all times.
Although the Domain Name System “officially” began in
1984 with the publication of RFC 920, the core of the new system was
described in 1983 in RFC 882 and RFC 883. From 1984 to 1987, the ARPAnet
(the precursor to today’s Internet) became a testbed of experimentation
for developing the new naming/addressing scheme in a rapidly expanding,
operational network environment. New RFCs were written and published in
1987 that modified the original documents to incorporate improvements
based on the working model. RFC 1034, “Domain Names-Concepts and
Facilities,” and RFC 1035, “Domain Names-Implementation and
Specification,” were published and became the standards upon which all
DNS implementations are built.
The first working domain name server, called “Jeeves,” was written in
1983-84 by Paul Mockapetris for operation on DEC Tops-20 machines
located at the University of Southern California’s Information Sciences
Institute (USC-ISI) and SRI International’s Network Information Center
(SRI-NIC). A DNS server for Unix machines, the Berkeley Internet Name
Domain (BIND) package, was written soon after by a group of graduate
students at the University of California at Berkeley under a grant from
the US Defense Advanced Research Projects Administration (DARPA).
Versions of BIND through 4.8.3 were maintained by the Computer Systems
Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark Painter, David
Riggle, and Songnian Zhou made up the initial BIND project team. After
that, additional work on the software package was done by Ralph
Campbell. Kevin Dunlap, a Digital Equipment Corporation employee on loan
to the CSRG, worked on BIND for 2 years, from 1985 to 1987. Many other
people also contributed to BIND development during that time: Doug
Kingston, Craig Partridge, Smoot Carl-Mitchell, Mike Muuss, Jim Bloom,
and Mike Schwartz. BIND maintenance was subsequently handled by Mike
Karels and Øivind Kure.
BIND versions 4.9 and 4.9.1 were released by Digital Equipment
Corporation (which became Compaq Computer Corporation and eventually merged
with Hewlett-Packard). Paul Vixie, then a DEC
employee, became BIND’s primary caretaker. He was assisted by Phil
Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan Beecher, Andrew
Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat Baran,
Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe Wolfhugel,
and others.
In 1994, BIND version 4.9.2 was sponsored by Vixie Enterprises. Paul
Vixie became BIND’s principal architect/programmer.
BIND versions from 4.9.3 onward have been developed and maintained by
Internet Systems Consortium and its predecessor, the Internet
Software Consortium, with support provided by ISC’s sponsors.
As co-architects/programmers, Bob Halley and Paul Vixie released the
first production-ready version of BIND version 8 in May 1997.
BIND version 9 was released in September 2000 and is a major rewrite of
nearly all aspects of the underlying BIND architecture.
BIND versions 4 and 8 are officially deprecated. No additional
development is done on BIND version 4 or BIND version 8.
BIND development work is made possible today by the sponsorship of
corporations who purchase professional support services from ISC
(https://www.isc.org/contact/) and/or donate to our mission, and by the
tireless efforts of numerous individuals.
While reading RFCs, please keep in mind that not all RFCs are
standards, and also that the validity of documents does change
over time. Every RFC needs to be interpreted in the context of other
documents.
BIND 9 strives for strict compliance with IETF standards. To the best
of our knowledge, BIND 9 complies with the following RFCs, with
the caveats and exceptions listed in the numbered notes below. Many
of these RFCs were written by current or former ISC staff members.
The list is non-exhaustive.
Some of these RFCs, though DNS-related, are not concerned with implementing
software.
RFC 1034 - P. Mockapetris. Domain Names — Concepts and Facilities. November
1987.
RFC 1035 - P. Mockapetris. Domain Names — Implementation and Specification.
November 1987. 12
RFC 1183 - C. F. Everhart, L. A. Mamakos, R. Ullmann, P. Mockapetris. New DNS RR
Definitions. October 1990.
RFC 1706 - B. Manning and R. Colella. DNS NSAP Resource Records. October 1994.
RFC 1712 - C. Farrell, M. Schulze, S. Pleitner, and D. Baldoni. DNS Encoding of
Geographical Location. November 1994.
RFC 1876 - C. Davis, P. Vixie, T. Goodwin, and I. Dickinson. A Means for Expressing
Location Information in the Domain Name System. January 1996.
RFC 1982 - R. Elz and R. Bush. Serial Number Arithmetic. August 1996.
RFC 1995 - M. Ohta. Incremental Zone Transfer in DNS. August 1996.
RFC 1996 - P. Vixie. A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY).
August 1996.
RFC 2136 - P. Vixie, S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates in the
Domain Name System (DNS UPDATE). April 1997.
RFC 2163 - A. Allocchio. Using the Internet DNS to Distribute MIXER
Conformant Global Address Mapping (MCGAM). January 1998.
RFC 2181 - R. Elz and R. Bush. Clarifications to the DNS Specification. July 1997.
RFC 2230 - R. Atkinson. Key Exchange Delegation Record for the DNS. November
1997.
RFC 2308 - M. Andrews. Negative Caching of DNS Queries (DNS NCACHE). March 1998.
RFC 2539 - D. Eastlake, 3rd. Storage of Diffie-Hellman Keys in the Domain Name
System (DNS). March 1999.
RFC 2782 - A. Gulbrandsen, P. Vixie, and L. Esibov. A DNS RR for Specifying the
Location of Services (DNS SRV). February 2000.
RFC 2930 - D. Eastlake, 3rd. Secret Key Establishment for DNS (TKEY RR).
September 2000.
RFC 2931 - D. Eastlake, 3rd. DNS Request and Transaction Signatures (SIG(0)s).
September 2000. 3
RFC 3007 - B. Wellington. Secure Domain Name System (DNS) Dynamic Update.
November 2000.
RFC 3110 - D. Eastlake, 3rd. RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
System (DNS). May 2001.
RFC 3123 - P. Koch. A DNS RR Type for Lists of Address Prefixes (APL RR). June
2001.
RFC 3225 - D. Conrad. Indicating Resolver Support of DNSSEC. December 2001.
RFC 3226 - O. Gudmundsson. DNSSEC and IPv6 A6 Aware Server/Resolver
Message Size Requirements. December 2001.
RFC 3363 - R. Bush, A. Durand, B. Fink, O. Gudmundsson, and T. Hain.
Representing Internet Protocol Version 6 (IPv6) Addresses in the Domain Name
System (DNS). August 2002. 15
RFC 3403 - M. Mealling.
Dynamic Delegation Discovery System (DDDS). Part Three: The Domain Name System
(DNS) Database.
October 2002.
RFC 3492 - A. Costello. Punycode: A Bootstring Encoding of Unicode for
Internationalized Domain Names in Applications (IDNA). March 2003.
RFC 3493 - R. Gilligan, S. Thomson, J. Bound, J. McCann, and W. Stevens.
Basic Socket Interface Extensions for IPv6. March 2003.
RFC 3496 - A. G. Malis and T. Hsiao. Protocol Extension for Support of
Asynchronous Transfer Mode (ATM) Service Class-aware Multiprotocol Label
Switching (MPLS) Traffic Engineering. March 2003.
RFC 3596 - S. Thomson, C. Huitema, V. Ksinant, and M. Souissi. DNS Extensions to
Support IP Version 6. October 2003.
RFC 3597 - A. Gustafsson. Handling of Unknown DNS Resource Record (RR) Types.
September 2003.
RFC 3645 - S. Kwan, P. Garg, J. Gilroy, L. Esibov, J. Westhead, and R. Hall. Generic
Security Service Algorithm for Secret Key Transaction Authentication for
DNS (GSS-TSIG). October 2003.
RFC 4025 - M. Richardson. A Method for Storing IPsec Keying Material in
DNS. March 2005.
RFC 4033 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. DNS Security
Introduction and Requirements. March 2005.
RFC 4034 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. Resource Records for
the DNS Security Extensions. March 2005.
RFC 4035 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. Protocol
Modifications for the DNS Security Extensions. March 2005.
RFC 4255 - J. Schlyter and W. Griffin. Using DNS to Securely Publish Secure
Shell (SSH) Key Fingerprints. January 2006.
RFC 4343 - D. Eastlake, 3rd. Domain Name System (DNS) Case Insensitivity
Clarification. January 2006.
RFC 4398 - S. Josefsson. Storing Certificates in the Domain Name System (DNS). March 2006.
RFC 4470 - S. Weiler and J. Ihren. Minimally covering NSEC Records and
DNSSEC On-line Signing. April 2006. 6
RFC 4509 - W. Hardaker. Use of SHA-256 in DNSSEC Delegation Signer
(DS) Resource Records (RRs). May 2006.
RFC 4592 - E. Lewis. The Role of Wildcards in the Domain Name System. July 2006.
RFC 4635 - D. Eastlake, 3rd. HMAC SHA (Hashed Message Authentication
Code, Secure Hash Algorithm) TSIG Algorithm Identifiers. August 2006.
RFC 4701 - M. Stapp, T. Lemon, and A. Gustafsson. A DNS Resource Record
(RR) for Encoding Dynamic Host Configuration Protocol (DHCP) Information (DHCID
RR). October 2006.
RFC 4955 - D. Blacka. DNS Security (DNSSEC) Experiments. July 2007. 7
RFC 5001 - R. Austein. DNS Name Server Identifier (NSID) Option. August 2007.
RFC 5011 - M. StJohns. Automated Updates of DNS Security (DNSSEC) Trust Anchors.
RFC 5155 - B. Laurie, G. Sisson, R. Arends, and D. Blacka. DNS Security
(DNSSEC) Hashed Authenticated Denial of Existence. March 2008.
RFC 5205 - P. Nikander and J. Laganier. Host Identity Protocol (HIP)
Domain Name System (DNS) Extension. April 2008.
RFC 5452 - A. Hubert and R. van Mook. Measures for Making DNS More
Resilient Against Forged Answers. January 2009. 8
RFC 5702 - J. Jansen. Use of SHA-2 Algorithms with RSA in DNSKEY and
RRSIG Resource Records for DNSSEC. October 2009.
RFC 5891 - J. Klensin.
Internationalized Domain Names in Applications (IDNA): Protocol.
August 2010
RFC 5936 - E. Lewis and A. Hoenes, Ed. DNS Zone Transfer Protocol (AXFR).
June 2010.
RFC 5952 - S. Kawamura and M. Kawashima. A Recommendation for IPv6 Address
Text Representation. August 2010.
RFC 6052 - C. Bao, C. Huitema, M. Bagnulo, M. Boucadair, and X. Li. IPv6
Addressing of IPv4/IPv6 Translators. October 2010.
RFC 6147 - M. Bagnulo, A. Sullivan, P. Matthews, and I. van Beijnum.
DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to
IPv4 Servers. April 2011. 9
RFC 6604 - D. Eastlake, 3rd. xNAME RCODE and Status Bits Clarification.
April 2012.
RFC 6605 - P. Hoffman and W. C. A. Wijngaards. Elliptic Curve Digital
Signature Algorithm (DSA) for DNSSEC. April 2012. 10
RFC 6672 - S. Rose and W. Wijngaards. DNAME Redirection in the DNS.
June 2012.
RFC 6698 - P. Hoffman and J. Schlyter. The DNS-Based Authentication of
Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA.
August 2012.
RFC 6725 - S. Rose. DNS Security (DNSSEC) DNSKEY Algorithm IANA Registry
Updates. August 2012. 11
RFC 6742 - RJ Atkinson, SN Bhatti, U. St. Andrews, and S. Rose. DNS
Resource Records for the Identifier-Locator Network Protocol (ILNP).
November 2012.
RFC 6840 - S. Weiler, Ed., and D. Blacka, Ed. Clarifications and
Implementation Notes for DNS Security (DNSSEC). February 2013. 12
RFC 6891 - J. Damas, M. Graff, and P. Vixie. Extension Mechanisms for DNS
(EDNS(0)). April 2013.
RFC 7043 - J. Abley. Resource Records for EUI-48 and EUI-64 Addresses
in the DNS. October 2013.
RFC 7208 - S. Kitterman.
Sender Policy Framework (SPF) for Authorizing Use of Domains in Email,
Version 1.
April 2014.
RFC 7314 - M. Andrews. Extension Mechanisms for DNS (EDNS) EXPIRE Option.
July 2014.
RFC 7344 - W. Kumari, O. Gudmundsson, and G. Barwood. Automating DNSSEC
Delegation Trust Maintenance. September 2014. 13
RFC 7477 - W. Hardaker. Child-to-Parent Synchronization in DNS. March
2015.
RFC 7553 - P. Faltstrom and O. Kolkman. The Uniform Resource Identifier
(URI) DNS Resource Record. June 2015.
RFC 7583 - S. Morris, J. Ihren, J. Dickinson, and W. Mekking. DNSSEC Key
Rollover Timing Considerations. October 2015.
RFC 7766 - J. Dickinson, S. Dickinson, R. Bellis, A. Mankin, and D.
Wessels. DNS Transport over TCP - Implementation Requirements. March 2016.
RFC 7828 - P. Wouters, J. Abley, S. Dickinson, and R. Bellis.
The edns-tcp-keepalive EDNS0 Option. April 2016.
RFC 7830 - A. Mayrhofer. The EDNS(0) Padding Option. May 2016. 14
RFC 7929 - P. Wouters. DNS-Based Authentication of Named Entities (DANE)
Bindings for OpenPGP. August 2016.
RFC 8078 - O. Gudmundsson and P. Wouters. Managing DS Records from the
Parent via CDS/CDNSKEY. March 2017. 20
RFC 8080 - O. Sury and R. Edmonds. Edwards-Curve Digital Security Algorithm
(EdDSA) for DNSSEC. February 2017.
RFC 8624 - P. Wouters and O. Sury. Algorithm Implementation Requirements
and Usage Guidance for DNSSEC. June 2019.
RFC 8659 - P. Hallam-Baker, R. Stradling, and J. Hoffman-Andrews.
DNS Certification Authority Authorization (CAA) Resource Record.
November 2019.
RFC 8945 - F. Dupont, S. Morris, P. Vixie, D. Eastlake 3rd, O. Gudmundsson,
and B. Wellington.
Secret Key Transaction Authentication for DNS (TSIG).
November 2020.
When receiving a query signed with a SIG(0), the server is
only able to verify the signature if it has the key in its local
authoritative data; it cannot do recursion or validation to
retrieve unknown keys.
Section 5.5 does not match reality. named uses the presence
of DO=1 to detect if validation may be occurring. CD has no bearing
on whether validation occurs.
Section 5.9 - Always set CD=1 on queries. This is not done, as
it prevents DNSSEC from working correctly through another recursive server.
When talking to a recursive server, the best algorithm is to send
CD=0 and then send CD=1 iff SERVFAIL is returned, in case the recursive
server has a bad clock and/or bad trust anchor. Alternatively, one
can send CD=1 then CD=0 on validation failure, in case the recursive
server is under attack or there is stale/bogus authoritative data.
This does not apply to DNS server implementations.
17
Only the Base 64 encoding specification is supported.
18
BIND 9 requires --with-libidn2 to enable entry of IDN labels within
dig, host, and nslookup at compile time. ACE labels are supported
everywhere with or without --with-libidn2.
Internet Drafts (IDs) are rough-draft working documents of the Internet
Engineering Task Force (IETF). They are, in essence, RFCs in the preliminary
stages of development. Implementors are cautioned not to regard IDs as
archival, and they should not be quoted or cited in any formal documents
unless accompanied by the disclaimer that they are “works in progress.”
IDs have a lifespan of six months, after which they are deleted unless
updated by their authors.
ddns-confgen is an utility that generates keys for use in TSIG signing.
The resulting keys can be used, for example, to secure dynamic DNS updates
to a zone, or for the rndc command channel.
The key name can specified using -k parameter and defaults to ddns-key.
The generated key is accompanied by configuration text and instructions that
can be used with nsupdate and named when setting up dynamic DNS,
including an example update-policy statement.
(This usage is similar to the rndc-confgen command for setting up
command-channel security.)
Note that named itself can configure a local DDNS key for use with
nsupdate-l; it does this when a zone is configured with
update-policylocal;. ddns-confgen is only needed when a more
elaborate configuration is required: for instance, if nsupdate is to
be used from a remote system.
This option specifies the algorithm to use for the TSIG key. Available
choices are: hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384,
and hmac-sha512. The default is hmac-sha256. Options are
case-insensitive, and the “hmac-” prefix may be omitted.
-h
This option prints a short summary of options and arguments.
-kkeyname
This option specifies the key name of the DDNS authentication key. The
default is ddns-key when neither the -s nor -z option is
specified; otherwise, the default is ddns-key as a separate label
followed by the argument of the option, e.g., ddns-key.example.com.
The key name must have the format of a valid domain name, consisting of
letters, digits, hyphens, and periods.
-q
This option enables quiet mode, which prints only the key, with no
explanatory text or usage examples. This is essentially identical to
tsig-keygen.
-sname
This option generates a configuration example to allow dynamic updates
of a single hostname. The example named.conf text shows how to set
an update policy for the specified name using the “name” nametype. The
default key name is ddns-key.name. Note that the “self” nametype
cannot be used, since the name to be updated may differ from the key
name. This option cannot be used with the -z option.
-zzone
This option generates a configuration example to allow
dynamic updates of a zone. The example named.conf text shows how
to set an update policy for the specified zone using the “zonesub”
nametype, allowing updates to all subdomain names within that zone.
This option cannot be used with the -s option.
delv is a tool for sending DNS queries and validating the results,
using the same internal resolver and validator logic as named.
delv sends to a specified name server all queries needed to
fetch and validate the requested data; this includes the original
requested query, subsequent queries to follow CNAME or DNAME chains,
queries for DNSKEY, and DS records to establish a chain of trust for
DNSSEC validation. It does not perform iterative resolution, but
simulates the behavior of a name server configured for DNSSEC validating
and forwarding.
By default, responses are validated using the built-in DNSSEC trust anchor
for the root zone (“.”). Records returned by delv are either fully
validated or were not signed. If validation fails, an explanation of the
failure is included in the output; the validation process can be traced
in detail. Because delv does not rely on an external server to carry
out validation, it can be used to check the validity of DNS responses in
environments where local name servers may not be trustworthy.
Unless it is told to query a specific name server, delv tries
each of the servers listed in /etc/resolv.conf. If no usable server
addresses are found, delv sends queries to the localhost
addresses (127.0.0.1 for IPv4, ::1 for IPv6).
When no command-line arguments or options are given, delv
performs an NS query for “.” (the root zone).
is the name or IP address of the name server to query. This can be an
IPv4 address in dotted-decimal notation or an IPv6 address in
colon-delimited notation. When the supplied server argument is a
hostname, delv resolves that name before querying that name
server (note, however, that this initial lookup is not validated by
DNSSEC).
If no server argument is provided, delv consults
/etc/resolv.conf; if an address is found there, it queries the
name server at that address. If either of the -4 or -6
options is in use, then only addresses for the corresponding
transport are tried. If no usable addresses are found, delv
sends queries to the localhost addresses (127.0.0.1 for IPv4, ::1
for IPv6).
name
is the domain name to be looked up.
type
indicates what type of query is required - ANY, A, MX, etc.
type can be any valid query type. If no type argument is
supplied, delv performs a lookup for an A record.
This option specifies a file from which to read DNSSEC trust anchors. The default
is /etc/bind.keys, which is included with BIND 9 and contains one
or more trust anchors for the root zone (“.”).
Keys that do not match the root zone name are ignored. An alternate
key name can be specified using the +root=NAME options.
Note: When reading the trust anchor file, delv treats trust-anchors,
initial-key, and static-key identically. That is, for a managed key,
it is the initial key that is trusted; RFC 5011 key management is not
supported. delv does not consult the managed-keys database maintained by
named, which means that if either of the keys in /etc/bind.keys is
revoked and rolled over, /etc/bind.keys must be updated to
use DNSSEC validation in delv.
-baddress
This option sets the source IP address of the query to address. This must be
a valid address on one of the host’s network interfaces, or 0.0.0.0,
or ::. An optional source port may be specified by appending
#<port>
-cclass
This option sets the query class for the requested data. Currently, only class
“IN” is supported in delv and any other value is ignored.
-dlevel
This option sets the systemwide debug level to level. The allowed range is
from 0 to 99. The default is 0 (no debugging). Debugging traces from
delv become more verbose as the debug level increases. See the
+mtrace, +rtrace, and +vtrace options below for
additional debugging details.
-h
This option displays the delv help usage output and exits.
-i
This option sets insecure mode, which disables internal DNSSEC validation. (Note,
however, that this does not set the CD bit on upstream queries. If the
server being queried is performing DNSSEC validation, then it does
not return invalid data; this can cause delv to time out. When it
is necessary to examine invalid data to debug a DNSSEC problem, use
dig+cd.)
-m
This option enables memory usage debugging.
-pport#
This option specifies a destination port to use for queries, instead of the
standard DNS port number 53. This option is used with a name
server that has been configured to listen for queries on a
non-standard port number.
-qname
This option sets the query name to name. While the query name can be
specified without using the -q option, it is sometimes necessary to
disambiguate names from types or classes (for example, when looking
up the name “ns”, which could be misinterpreted as the type NS, or
“ch”, which could be misinterpreted as class CH).
-ttype
This option sets the query type to type, which can be any valid query type
supported in BIND 9 except for zone transfer types AXFR and IXFR. As
with -q, this is useful to distinguish query-name types or classes
when they are ambiguous. It is sometimes necessary to disambiguate
names from types.
The default query type is “A”, unless the -x option is supplied
to indicate a reverse lookup, in which case it is “PTR”.
-v
This option prints the delv version and exits.
-xaddr
This option performs a reverse lookup, mapping an address to a name. addr
is an IPv4 address in dotted-decimal notation, or a colon-delimited
IPv6 address. When -x is used, there is no need to provide the
name or type arguments; delv automatically performs a
lookup for a name like 11.12.13.10.in-addr.arpa and sets the
query type to PTR. IPv6 addresses are looked up using nibble format
under the IP6.ARPA domain.
delv provides a number of query options which affect the way results
are displayed, and in some cases the way lookups are performed.
Each query option is identified by a keyword preceded by a plus sign
(+). Some keywords set or reset an option. These may be preceded by
the string no to negate the meaning of that keyword. Other keywords
assign values to options like the timeout interval. They have the form
+keyword=value. The query options are:
+[no]cdflag
This option controls whether to set the CD (checking disabled) bit in queries
sent by delv. This may be useful when troubleshooting DNSSEC
problems from behind a validating resolver. A validating resolver
blocks invalid responses, making it difficult to retrieve them
for analysis. Setting the CD flag on queries causes the resolver
to return invalid responses, which delv can then validate
internally and report the errors in detail.
+[no]class
This option controls whether to display the CLASS when printing a record. The
default is to display the CLASS.
+[no]ttl
This option controls whether to display the TTL when printing a record. The
default is to display the TTL.
+[no]rtrace
This option toggles resolver fetch logging. This reports the name and type of each
query sent by delv in the process of carrying out the resolution
and validation process, including the original query
and all subsequent queries to follow CNAMEs and to establish a chain
of trust for DNSSEC validation.
This is equivalent to setting the debug level to 1 in the “resolver”
logging category. Setting the systemwide debug level to 1 using the
-d option produces the same output, but affects other
logging categories as well.
+[no]mtrace
This option toggles message logging. This produces a detailed dump of the
responses received by delv in the process of carrying out the
resolution and validation process.
This is equivalent to setting the debug level to 10 for the “packets”
module of the “resolver” logging category. Setting the systemwide
debug level to 10 using the -d option produces the same
output, but affects other logging categories as well.
+[no]vtrace
This option toggles validation logging. This shows the internal process of the
validator as it determines whether an answer is validly signed,
unsigned, or invalid.
This is equivalent to setting the debug level to 3 for the
“validator” module of the “dnssec” logging category. Setting the
systemwide debug level to 3 using the -d option produces the
same output, but affects other logging categories as well.
+[no]short
This option toggles between verbose and terse answers. The default is to print the answer in a
verbose form.
+[no]comments
This option toggles the display of comment lines in the output. The default is to
print comments.
+[no]rrcomments
This option toggles the display of per-record comments in the output (for example,
human-readable key information about DNSKEY records). The default is
to print per-record comments.
+[no]crypto
This option toggles the display of cryptographic fields in DNSSEC records. The
contents of these fields are unnecessary to debug most DNSSEC
validation failures and removing them makes it easier to see the
common failures. The default is to display the fields. When omitted,
they are replaced by the string [omitted] or, in the DNSKEY case, the
key ID is displayed as the replacement, e.g. [keyid=value].
+[no]trust
This option controls whether to display the trust level when printing a record.
The default is to display the trust level.
+[no]split[=W]
This option splits long hex- or base64-formatted fields in resource records into
chunks of W characters (where W is rounded up to the nearest
multiple of 4). +nosplit or +split=0 causes fields not to be
split at all. The default is 56 characters, or 44 characters when
multiline mode is active.
+[no]all
This option sets or clears the display options +[no]comments,
+[no]rrcomments, and +[no]trust as a group.
+[no]multiline
This option prints long records (such as RRSIG, DNSKEY, and SOA records) in a
verbose multi-line format with human-readable comments. The default
is to print each record on a single line, to facilitate machine
parsing of the delv output.
+[no]dnssec
This option indicates whether to display RRSIG records in the delv output.
The default is to do so. Note that (unlike in dig) this does
not control whether to request DNSSEC records or to
validate them. DNSSEC records are always requested, and validation
always occurs unless suppressed by the use of -i or
+noroot.
+[no]root[=ROOT]
This option indicates whether to perform conventional DNSSEC validation, and if so,
specifies the name of a trust anchor. The default is to validate using a
trust anchor of “.” (the root zone), for which there is a built-in key. If
specifying a different trust anchor, then -a must be used to specify a
file containing the key.
+[no]tcp
This option controls whether to use TCP when sending queries. The default is to
use UDP unless a truncated response has been received.
+[no]unknownformat
This option prints all RDATA in unknown RR-type presentation format (RFC 3597).
The default is to print RDATA for known types in the type’s
presentation format.
dig is a flexible tool for interrogating DNS name servers. It
performs DNS lookups and displays the answers that are returned from the
name server(s) that were queried. Most DNS administrators use dig to
troubleshoot DNS problems because of its flexibility, ease of use, and
clarity of output. Other lookup tools tend to have less functionality
than dig.
Although dig is normally used with command-line arguments, it also
has a batch mode of operation for reading lookup requests from a file. A
brief summary of its command-line arguments and options is printed when
the -h option is given. The BIND 9
implementation of dig allows multiple lookups to be issued from the
command line.
Unless it is told to query a specific name server, dig tries each
of the servers listed in /etc/resolv.conf. If no usable server
addresses are found, dig sends the query to the local host.
When no command-line arguments or options are given, dig
performs an NS query for “.” (the root).
It is possible to set per-user defaults for dig via
${HOME}/.digrc. This file is read and any options in it are applied
before the command-line arguments. The -r option disables this
feature, for scripts that need predictable behavior.
The IN and CH class names overlap with the IN and CH top-level domain
names. Either use the -t and -c options to specify the type and
class, use the -q to specify the domain name, or use “IN.” and
“CH.” when looking up these top-level domains.
is the name or IP address of the name server to query. This can be an
IPv4 address in dotted-decimal notation or an IPv6 address in
colon-delimited notation. When the supplied server argument is a
hostname, dig resolves that name before querying that name
server.
If no server argument is provided, dig consults
/etc/resolv.conf; if an address is found there, it queries the
name server at that address. If either of the -4 or -6
options are in use, then only addresses for the corresponding
transport are tried. If no usable addresses are found, dig
sends the query to the local host. The reply from the name server
that responds is displayed.
name
is the name of the resource record that is to be looked up.
type
indicates what type of query is required - ANY, A, MX, SIG, etc.
type can be any valid query type. If no type argument is
supplied, dig performs a lookup for an A record.
This option indicates that only IPv4 should be used.
-6
This option indicates that only IPv6 should be used.
-baddress[#port]
This option sets the source IP address of the query. The address must be a
valid address on one of the host’s network interfaces, or “0.0.0.0”
or “::”. An optional port may be specified by appending #port.
-cclass
This option sets the query class. The default class is IN; other classes are
HS for Hesiod records or CH for Chaosnet records.
-ffile
This option sets batch mode, in which dig reads a list of lookup requests to process from
the given file. Each line in the file should be organized in the
same way it would be presented as a query to dig using the
command-line interface.
-kkeyfile
This option tells named to sign queries using TSIG using a key read from the given file. Key
files can be generated using tsig-keygen. When using TSIG
authentication with dig, the name server that is queried needs to
know the key and algorithm that is being used. In BIND, this is done
by providing appropriate key and server statements in
named.conf.
-m
This option enables memory usage debugging.
-pport
This option sends the query to a non-standard port on the server, instead of the
default port 53. This option is used to test a name server that
has been configured to listen for queries on a non-standard port
number.
-qname
This option specifies the domain name to query. This is useful to distinguish the name
from other arguments.
-r
This option indicates that options from ${HOME}/.digrc should not be read. This is useful for
scripts that need predictable behavior.
-ttype
This option indicates the resource record type to query, which can be any valid query type. If
it is a resource record type supported in BIND 9, it can be given by
the type mnemonic (such as NS or AAAA). The default query type is
A, unless the -x option is supplied to indicate a reverse
lookup. A zone transfer can be requested by specifying a type of
AXFR. When an incremental zone transfer (IXFR) is required, set the
type to ixfr=N. The incremental zone transfer contains
all changes made to the zone since the serial number in the zone’s
SOA record was N.
All resource record types can be expressed as TYPEnn, where nn is
the number of the type. If the resource record type is not supported
in BIND 9, the result is displayed as described in RFC 3597.
-u
This option indicates that print query times should be provided in microseconds instead of milliseconds.
-v
This option prints the version number and exits.
-xaddr
This option sets simplified reverse lookups, for mapping addresses to names. The
addr is an IPv4 address in dotted-decimal notation, or a
colon-delimited IPv6 address. When the -x option is used, there is no
need to provide the name, class, and type arguments.
dig automatically performs a lookup for a name like
94.2.0.192.in-addr.arpa and sets the query type and class to PTR
and IN respectively. IPv6 addresses are looked up using nibble format
under the IP6.ARPA domain.
-y[hmac:]keyname:secret
This option signs queries using TSIG with the given authentication key.
keyname is the name of the key, and secret is the
base64-encoded shared secret. hmac is the name of the key algorithm;
valid choices are hmac-md5, hmac-sha1, hmac-sha224,
hmac-sha256, hmac-sha384, or hmac-sha512. If hmac is
not specified, the default is hmac-md5; if MD5 was disabled, the default is
hmac-sha256.
Note
Only the -k option should be used, rather than the -y option,
because with -y the shared secret is supplied as a command-line
argument in clear text. This may be visible in the output from ps1 or
in a history file maintained by the user’s shell.
dig provides a number of query options which affect the way in which
lookups are made and the results displayed. Some of these set or reset
flag bits in the query header, some determine which sections of the
answer get printed, and others determine the timeout and retry
strategies.
Each query option is identified by a keyword preceded by a plus sign
(+). Some keywords set or reset an option; these may be preceded by
the string no to negate the meaning of that keyword. Other keywords
assign values to options, like the timeout interval. They have the form
+keyword=value. Keywords may be abbreviated, provided the
abbreviation is unambiguous; for example, +cd is equivalent to
+cdflag. The query options are:
+[no]aaflag
This option is a synonym for +[no]aaonly.
+[no]aaonly
This option sets the aa flag in the query.
+[no]additional
This option displays [or does not display] the additional section of a reply. The
default is to display it.
+[no]adflag
This option sets [or does not set] the AD (authentic data) bit in the query. This
requests the server to return whether all of the answer and authority
sections have been validated as secure, according to the security
policy of the server. AD=1 indicates that all records have been
validated as secure and the answer is not from a OPT-OUT range. AD=0
indicates that some part of the answer was insecure or not validated.
This bit is set by default.
+[no]all
This option sets or clears all display flags.
+[no]answer
This option displays [or does not display] the answer section of a reply. The default
is to display it.
+[no]authority
This option displays [or does not display] the authority section of a reply. The
default is to display it.
+[no]badcookie
This option retries the lookup with a new server cookie if a BADCOOKIE response is
received.
+[no]besteffort
This option attempts to display the contents of messages which are malformed. The
default is to not display malformed answers.
+bufsize[=B]
This option sets the UDP message buffer size advertised using EDNS0
to B bytes. The maximum and minimum sizes of this buffer are
65535 and 0, respectively. +bufsize=0 disables EDNS (use
+bufsize=0+edns to send an EDNS message with an advertised size
of 0 bytes). +bufsize restores the default buffer size.
+[no]cdflag
This option sets [or does not set] the CD (checking disabled) bit in the query. This
requests the server to not perform DNSSEC validation of responses.
+[no]class
This option displays [or does not display] the CLASS when printing the record.
+[no]cmd
This option toggles the printing of the initial comment in the output, identifying the
version of dig and the query options that have been applied. This option
always has a global effect; it cannot be set globally and then overridden on a
per-lookup basis. The default is to print this comment.
+[no]comments
This option toggles the display of some comment lines in the output, with
information about the packet header and OPT pseudosection, and the names of
the response section. The default is to print these comments.
Other types of comments in the output are not affected by this option, but
can be controlled using other command-line switches. These include
+[no]cmd, +[no]question, +[no]stats, and +[no]rrcomments.
+[no]cookie=####
This option sends [or does not send] a COOKIE EDNS option, with an optional value. Replaying a COOKIE
from a previous response allows the server to identify a previous
client. The default is +cookie.
+cookie is also set when +trace is set to better emulate the
default queries from a nameserver.
+[no]crypto
This option toggles the display of cryptographic fields in DNSSEC records. The
contents of these fields are unnecessary for debugging most DNSSEC
validation failures and removing them makes it easier to see the
common failures. The default is to display the fields. When omitted,
they are replaced by the string [omitted] or, in the DNSKEY case, the
key ID is displayed as the replacement, e.g. [keyid=value].
+[no]defname
This option, which is deprecated, is treated as a synonym for +[no]search.
+[no]dnssec
This option requests that DNSSEC records be sent by setting the DNSSEC OK (DO) bit in
the OPT record in the additional section of the query.
+domain=somename
This option sets the search list to contain the single domain somename, as if
specified in a domain directive in /etc/resolv.conf, and
enables search list processing as if the +search option were
given.
+dscp=value
This option sets the DSCP code point to be used when sending the query. Valid DSCP
code points are in the range [0…63]. By default no code point is
explicitly set.
+[no]edns[=#]
This option specifies the EDNS version to query with. Valid values are 0 to 255.
Setting the EDNS version causes an EDNS query to be sent.
+noedns clears the remembered EDNS version. EDNS is set to 0 by
default.
+[no]ednsflags[=#]
This option sets the must-be-zero EDNS flags bits (Z bits) to the specified value.
Decimal, hex, and octal encodings are accepted. Setting a named flag
(e.g., DO) is silently ignored. By default, no Z bits are set.
+[no]ednsnegotiation
This option enables/disables EDNS version negotiation. By default, EDNS version
negotiation is enabled.
+[no]ednsopt[=code[:value]]
This option specifies the EDNS option with code point code and an optional payload
of value as a hexadecimal string. code can be either an EDNS
option name (for example, NSID or ECS) or an arbitrary
numeric value. +noednsopt clears the EDNS options to be sent.
+[no]expire
This option sends an EDNS Expire option.
+[no]fail
This option indicates that named should try [or not try] the next server if a SERVFAIL is received. The default is
to not try the next server, which is the reverse of normal stub
resolver behavior.
+[no]header-only
This option sends a query with a DNS header without a question section. The
default is to add a question section. The query type and query name
are ignored when this is set.
+[no]identify
This option shows [or does not show] the IP address and port number that supplied
the answer, when the +short option is enabled. If short form
answers are requested, the default is not to show the source address
and port number of the server that provided the answer.
+[no]idnin
This option processes [or does not process] IDN domain names on input. This requires
IDNSUPPORT to have been enabled at compile time.
The default is to process IDN input when standard output is a tty.
The IDN processing on input is disabled when dig output is redirected
to files, pipes, and other non-tty file descriptors.
+[no]idnout
This option converts [or does not convert] puny code on output. This requires
IDNSUPPORT to have been enabled at compile time.
The default is to process puny code on output when standard output is
a tty. The puny code processing on output is disabled when dig output
is redirected to files, pipes, and other non-tty file descriptors.
+[no]ignore
This option ignores [or does not ignore] truncation in UDP responses instead of retrying with TCP. By
default, TCP retries are performed.
+[no]keepalive
This option sends [or does not send] an EDNS Keepalive option.
+[no]keepopen
This option keeps [or does not keep] the TCP socket open between queries, and reuses it rather than
creating a new TCP socket for each lookup. The default is
+nokeepopen.
+[no]mapped
This option allows [or does not allow] mapped IPv4-over-IPv6 addresses to be used. The default is
+mapped.
+[no]multiline
This option prints [or does not print] records, like the SOA records, in a verbose multi-line format
with human-readable comments. The default is to print each record on
a single line to facilitate machine parsing of the dig output.
+ndots=D
This option sets the number of dots (D) that must appear in name for
it to be considered absolute. The default value is that defined using
the ndots statement in /etc/resolv.conf, or 1 if no ndots
statement is present. Names with fewer dots are interpreted as
relative names, and are searched for in the domains listed in the
search or domain directive in /etc/resolv.conf if
+search is set.
+[no]nsid
When enabled, this option includes an EDNS name server ID request when sending a query.
+[no]nssearch
When this option is set, dig attempts to find the authoritative
name servers for the zone containing the name being looked up, and
display the SOA record that each name server has for the zone.
Addresses of servers that did not respond are also printed.
+[no]onesoa
When enabled, this option prints only one (starting) SOA record when performing an AXFR. The
default is to print both the starting and ending SOA records.
+[no]opcode=value
When enabled, this option sets (restores) the DNS message opcode to the specified value. The
default value is QUERY (0).
+padding=value
This option pads the size of the query packet using the EDNS Padding option to
blocks of value bytes. For example, +padding=32 causes a
48-byte query to be padded to 64 bytes. The default block size is 0,
which disables padding; the maximum is 512. Values are ordinarily
expected to be powers of two, such as 128; however, this is not
mandatory. Responses to padded queries may also be padded, but only
if the query uses TCP or DNS COOKIE.
+[no]qr
This option toggles the display of the query message as it is sent. By default, the query
is not printed.
+[no]question
This option toggles the display of the question section of a query when an answer is
returned. The default is to print the question section as a comment.
+[no]raflag
This option sets [or does not set] the RA (Recursion Available) bit in the query. The
default is +noraflag. This bit is ignored by the server for
QUERY.
+[no]rdflag
This option is a synonym for +[no]recurse.
+[no]recurse
This option toggles the setting of the RD (recursion desired) bit in the query.
This bit is set by default, which means dig normally sends
recursive queries. Recursion is automatically disabled when the
+nssearch or +trace query option is used.
+retry=T
This option sets the number of times to retry UDP and TCP queries to server to T
instead of the default, 2. Unlike +tries, this does not include
the initial query.
+[no]rrcomments
This option toggles the display of per-record comments in the output (for example,
human-readable key information about DNSKEY records). The default is
not to print record comments unless multiline mode is active.
+[no]search
This option uses [or does not use] the search list defined by the searchlist or domain
directive in resolv.conf, if any. The search list is not used by
default.
ndots from resolv.conf (default 1), which may be overridden by
+ndots, determines whether the name is treated as relative
and hence whether a search is eventually performed.
+[no]short
This option toggles whether a terse answer is provided. The default is to print the answer in a verbose
form. This option always has a global effect; it cannot be set globally and
then overridden on a per-lookup basis.
+[no]showsearch
This option performs [or does not perform] a search showing intermediate results.
+[no]sigchase
This feature is now obsolete and has been removed; use delv
instead.
+split=W
This option splits long hex- or base64-formatted fields in resource records into
chunks of W characters (where W is rounded up to the nearest
multiple of 4). +nosplit or +split=0 causes fields not to be
split at all. The default is 56 characters, or 44 characters when
multiline mode is active.
+[no]stats
This option toggles the printing of statistics: when the query was made, the size of the
reply, etc. The default behavior is to print the query statistics as a
comment after each lookup.
+[no]subnet=addr[/prefix-length]
This option sends [or does not send] an EDNS CLIENT-SUBNET option with the specified IP
address or network prefix.
dig+subnet=0.0.0.0/0, or simply dig+subnet=0 for short,
sends an EDNS CLIENT-SUBNET option with an empty address and a source
prefix-length of zero, which signals a resolver that the client’s
address information must not be used when resolving this query.
+[no]tcflag
This option sets [or does not set] the TC (TrunCation) bit in the query. The default is
+notcflag. This bit is ignored by the server for QUERY.
+[no]tcp
This option uses [or does not use] TCP when querying name servers.
The default behavior is to use UDP unless a type any or
ixfr=N query is requested, in which case the default is TCP.
AXFR queries always use TCP. To prevent retry over TCP when TC=1
is returned from a UDP query, use +ignore.
+timeout=T
This option sets the timeout for a query to T seconds. The default timeout is
5 seconds. An attempt to set T to less than 1 is silently set to 1.
+[no]topdown
This feature is related to dig+sigchase, which is obsolete and
has been removed. Use delv instead.
+[no]trace
This option toggles tracing of the delegation path from the root name servers for
the name being looked up. Tracing is disabled by default. When
tracing is enabled, dig makes iterative queries to resolve the
name being looked up. It follows referrals from the root servers,
showing the answer from each server that was used to resolve the
lookup.
If @server is also specified, it affects only the initial query for
the root zone name servers.
+dnssec is also set when +trace is set, to better emulate the
default queries from a name server.
+tries=T
This option sets the number of times to try UDP and TCP queries to server to T
instead of the default, 3. If T is less than or equal to zero,
the number of tries is silently rounded up to 1.
+trusted-key=####
This option formerly specified trusted keys for use with dig+sigchase. This
feature is now obsolete and has been removed; use delv instead.
+[no]ttlid
This option displays [or does not display] the TTL when printing the record.
+[no]ttlunits
This option displays [or does not display] the TTL in friendly human-readable time
units of s, m, h, d, and w, representing seconds, minutes,
hours, days, and weeks. This implies +ttlid.
+[no]unexpected
This option accepts [or does not accept] answers from unexpected sources. By default, dig
will not accept a reply from a source other than the one to which it sent the
query.
+[no]unknownformat
This option prints all RDATA in unknown RR type presentation format (RFC 3597).
The default is to print RDATA for known types in the type’s
presentation format.
+[no]vc
This option uses [or does not use] TCP when querying name servers. This alternate
syntax to +[no]tcp is provided for backwards compatibility. The
vc stands for “virtual circuit.”
+[no]yaml
When enabled, this option prints the responses (and, if +qr is in use, also the
outgoing queries) in a detailed YAML format.
+[no]zflag
This option sets [or does not set] the last unassigned DNS header flag in a DNS query.
This flag is off by default.
The BIND 9 implementation of dig supports specifying multiple
queries on the command line (in addition to supporting the -f batch
file option). Each of those queries can be supplied with its own set of
flags, options, and query options.
In this case, each query argument represents an individual query in
the command-line syntax described above. Each consists of any of the
standard options and flags, the name to be looked up, an optional query
type and class, and any query options that should be applied to that
query.
A global set of query options, which should be applied to all queries,
can also be supplied. These global query options must precede the first
tuple of name, class, type, options, flags, and query options supplied
on the command line. Any global query options (except +[no]cmd and
+[no]short options) can be overridden by a query-specific set of
query options. For example:
dig+qrwww.isc.organy-x127.0.0.1isc.orgns+noqr
shows how dig can be used from the command line to make three
lookups: an ANY query for www.isc.org, a reverse lookup of 127.0.0.1,
and a query for the NS records of isc.org. A global query option of
+qr is applied, so that dig shows the initial query it made for
each lookup. The final query has a local query option of +noqr which
means that dig does not print the initial query when it looks up the
NS records for isc.org.
If dig has been built with IDN (internationalized domain name)
support, it can accept and display non-ASCII domain names. dig
appropriately converts character encoding of a domain name before sending
a request to a DNS server or displaying a reply from the server.
To turn off IDN support, use the parameters
+noidnin and +noidnout, or define the IDN_DISABLE environment
variable.
The dnssec-cds command changes DS records at a delegation point
based on CDS or CDNSKEY records published in the child zone. If both CDS
and CDNSKEY records are present in the child zone, the CDS is preferred.
This enables a child zone to inform its parent of upcoming changes to
its key-signing keys (KSKs); by polling periodically with dnssec-cds, the
parent can keep the DS records up-to-date and enable automatic rolling
of KSKs.
Two input files are required. The -fchild-file option specifies a
file containing the child’s CDS and/or CDNSKEY records, plus RRSIG and
DNSKEY records so that they can be authenticated. The -dpath option
specifies the location of a file containing the current DS records. For
example, this could be a dsset- file generated by
dnssec-signzone, or the output of dnssec-dsfromkey, or the
output of a previous run of dnssec-cds.
The dnssec-cds command uses special DNSSEC validation logic
specified by RFC 7344. It requires that the CDS and/or CDNSKEY records
be validly signed by a key represented in the existing DS records. This
is typically the pre-existing KSK.
For protection against replay attacks, the signatures on the child
records must not be older than they were on a previous run of
dnssec-cds. Their age is obtained from the modification time of the
dsset- file, or from the -s option.
To protect against breaking the delegation, dnssec-cds ensures that
the DNSKEY RRset can be verified by every key algorithm in the new DS
RRset, and that the same set of keys are covered by every DS digest
type.
By default, replacement DS records are written to the standard output;
with the -i option the input file is overwritten in place. The
replacement DS records are the same as the existing records, when no
change is required. The output can be empty if the CDS/CDNSKEY records
specify that the child zone wants to be insecure.
Warning
Be careful not to delete the DS records when dnssec-cds fails!
Alternatively, dnssec-cds-u writes an nsupdate script to the
standard output. The -u and -i options can be used together to
maintain a dsset- file as well as emit an nsupdate script.
This option specifies a digest algorithm to use when converting CDNSKEY records to
DS records. This option can be repeated, so that multiple DS records
are created for each CDNSKEY record. This option has no effect when
using CDS records.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These values
are case-insensitive, and the hyphen may be omitted. If no algorithm
is specified, the default is SHA-256.
-cclass
This option specifies the DNS class of the zones.
-D
This option generates DS records from CDNSKEY records if both CDS and CDNSKEY
records are present in the child zone. By default CDS records are
preferred.
-dpath
This specifies the location of the parent DS records. The path can be the name of a file
containing the DS records; if it is a directory, dnssec-cds
looks for a dsset- file for the domain inside the directory.
To protect against replay attacks, child records are rejected if they
were signed earlier than the modification time of the dsset-
file. This can be adjusted with the -s option.
-fchild-file
This option specifies the file containing the child’s CDS and/or CDNSKEY records, plus its
DNSKEY records and the covering RRSIG records, so that they can be
authenticated.
The examples below describe how to generate this file.
-iextension
This option updates the dsset- file in place, instead of writing DS records to
the standard output.
There must be no space between the -i and the extension. If
no extension is provided, the old dsset- is discarded. If an
extension is present, a backup of the old dsset- file is kept
with the extension appended to its filename.
To protect against replay attacks, the modification time of the
dsset- file is set to match the signature inception time of the
child records, provided that it is later than the file’s current
modification time.
-sstart-time
This option specifies the date and time after which RRSIG records become
acceptable. This can be either an absolute or a relative time. An
absolute start time is indicated by a number in YYYYMMDDHHMMSS
notation; 20170827133700 denotes 13:37:00 UTC on August 27th, 2017. A
time relative to the dsset- file is indicated with -N, which is N
seconds before the file modification time. A time relative to the
current time is indicated with now+N.
If no start-time is specified, the modification time of the
dsset- file is used.
-Tttl
This option specifies a TTL to be used for new DS records. If not specified, the
default is the TTL of the old DS records. If they had no explicit TTL,
the new DS records also have no explicit TTL.
-u
This option writes an nsupdate script to the standard output, instead of
printing the new DS reords. The output is empty if no change is
needed.
Note: The TTL of new records needs to be specified: it can be done in the
original dsset- file, with the -T option, or using the
nsupdatettl command.
-V
This option prints version information.
-vlevel
This option sets the debugging level. Level 1 is intended to be usefully verbose
for general users; higher levels are intended for developers.
domain
This indicates the name of the delegation point/child zone apex.
Before running dnssec-signzone, ensure that the delegations
are up-to-date by running dnssec-cds on every dsset- file.
To fetch the child records required by dnssec-cds, invoke
dig as in the script below. It is acceptable if the dig fails, since
dnssec-cds performs all the necessary checking.
for f in dsset-*
do
d=${f#dsset-}
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
dnssec-cds -i -f /dev/stdin -d $f $d
done
When the parent zone is automatically signed by named,
dnssec-cds can be used with nsupdate to maintain a delegation as follows.
The dsset- file allows the script to avoid having to fetch and
validate the parent DS records, and it maintains the replay attack
protection time.
This option specifies a digest algorithm to use when converting DNSKEY records to
DS records. This option can be repeated, so that multiple DS records
are created for each DNSKEY record.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These values
are case-insensitive, and the hyphen may be omitted. If no algorithm
is specified, the default is SHA-256.
-A
This option indicates that ZSKs are to be included when generating DS records. Without this option, only
keys which have the KSK flag set are converted to DS records and
printed. This option is only useful in -f zone file mode.
-cclass
This option specifies the DNS class; the default is IN. This option is only useful in -s keyset
or -f zone file mode.
-C
This option generates CDS records rather than DS records.
-ffile
This option sets zone file mode, in which the final dnsname argument of dnssec-dsfromkey is the
DNS domain name of a zone whose master file can be read from
file. If the zone name is the same as file, then it may be
omitted.
If file is -, then the zone data is read from the standard
input. This makes it possible to use the output of the dig
command as input, as in:
dnssec-importkey reads a public DNSKEY record and generates a pair
of .key/.private files. The DNSKEY record may be read from an
existing .key file, in which case a corresponding .private file is
generated, or it may be read from any other file or from the standard
input, in which case both .key and .private files are generated.
The newly created .private file does not contain private key data, and
cannot be used for signing. However, having a .private file makes it
possible to set publication (-P) and deletion (-D) times for the
key, which means the public key can be added to and removed from the
DNSKEY RRset on schedule even if the true private key is stored offline.
This option indicates the zone file mode. Instead of a public keyfile name, the argument is the
DNS domain name of a zone master file, which can be read from
filename. If the domain name is the same as filename, then it may be
omitted.
If filename is set to "-", then the zone data is read from the
standard input.
-Kdirectory
This option sets the directory in which the key files are to reside.
-Lttl
This option sets the default TTL to use for this key when it is converted into a
DNSKEY RR. This is the TTL used when the key is imported into a zone,
unless there was already a DNSKEY RRset in
place, in which case the existing TTL takes precedence. Setting the default TTL to 0 or none
removes it from the key.
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS. If the
argument begins with a + or -, it is interpreted as an offset from
the present time. For convenience, if such an offset is followed by one
of the suffixes y, mo, w, d, h, or mi, then the offset is
computed in years (defined as 365 24-hour days, ignoring leap years),
months (defined as 30 24-hour days), weeks, days, hours, or minutes,
respectively. Without a suffix, the offset is computed in seconds. To
explicitly prevent a date from being set, use none or never.
-Pdate/offset
This option sets the date on which a key is to be published to the zone. After
that date, the key is included in the zone but is not used
to sign it.
-Psyncdate/offset
This option sets the date on which CDS and CDNSKEY records that match this key
are to be published to the zone.
-Ddate/offset
This option sets the date on which the key is to be deleted. After that date, the
key is no longer included in the zone. (However, it may remain in the key
repository.)
-Dsyncdate/offset
This option sets the date on which the CDS and CDNSKEY records that match this
key are to be deleted.
Specify a digest algorithm to use when converting the zones DNSKEY
records to expected DS records. This option can be repeated, so that
multiple records are checked for each DNSKEY record.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These
values are case insensitive, and the hyphen may be omitted. If no
algorithm is specified, the default is SHA-256.
-ffile
If a file is specified, then the zone is read from that file to
find the DNSKEY records. If not, then the DNSKEY records for the zone
are looked up in the DNS.
-sfile
Specifies a prepared dsset file, such as would be generated by
dnssec-signzone, to use as a source for the DS RRset instead of
querying the parent.
-ddig path
Specifies a path to a dig binary. Used for testing.
-Ddsfromkey path
Specifies a path to a dnssec-dsfromkey binary. Used for testing.
dnssec-coverage verifies that the DNSSEC keys for a given zone or a
set of zones have timing metadata set properly to ensure no future
lapses in DNSSEC coverage.
If zone is specified, then keys found in the key repository matching
that zone are scanned, and an ordered list is generated of the events
scheduled for that key (i.e., publication, activation, inactivation,
deletion). The list of events is walked in order of occurrence. Warnings
are generated if any event is scheduled which could cause the zone to
enter a state in which validation failures might occur: for example, if
the number of published or active keys for a given algorithm drops to
zero, or if a key is deleted from the zone too soon after a new key is
rolled, and cached data signed by the prior key has not had time to
expire from resolver caches.
If zone is not specified, then all keys in the key repository will
be scanned, and all zones for which there are keys will be analyzed.
(Note: This method of reporting is only accurate if all the zones that
have keys in a given repository share the same TTL parameters.)
Sets the directory in which keys can be found. Defaults to the
current working directory.
-ffile
If a file is specified, then the zone is read from that file; the
largest TTL and the DNSKEY TTL are determined directly from the zone
data, and the -m and -d options do not need to be specified
on the command line.
-lduration
The length of time to check for DNSSEC coverage. Key events scheduled
further into the future than duration will be ignored, and
assumed to be correct.
The value of duration can be set in seconds, or in larger units
of time by adding a suffix: mi for minutes, h for hours, d for days,
w for weeks, mo for months, y for years.
-mmaximum TTL
Sets the value to be used as the maximum TTL for the zone or zones
being analyzed when determining whether there is a possibility of
validation failure. When a zone-signing key is deactivated, there
must be enough time for the record in the zone with the longest TTL
to have expired from resolver caches before that key can be purged
from the DNSKEY RRset. If that condition does not apply, a warning
will be generated.
The length of the TTL can be set in seconds, or in larger units of
time by adding a suffix: mi for minutes, h for hours, d for days, w
for weeks, mo for months, y for years.
This option is not necessary if the -f has been used to specify a
zone file. If -f has been specified, this option may still be
used; it will override the value found in the file.
If this option is not used and the maximum TTL cannot be retrieved
from a zone file, a warning is generated and a default value of 1
week is used.
-dDNSKEY TTL
Sets the value to be used as the DNSKEY TTL for the zone or zones
being analyzed when determining whether there is a possibility of
validation failure. When a key is rolled (that is, replaced with a
new key), there must be enough time for the old DNSKEY RRset to have
expired from resolver caches before the new key is activated and
begins generating signatures. If that condition does not apply, a
warning will be generated.
The length of the TTL can be set in seconds, or in larger units of
time by adding a suffix: mi for minutes, h for hours, d for days, w
for weeks, mo for months, y for years.
This option is not necessary if -f has been used to specify a
zone file from which the TTL of the DNSKEY RRset can be read, or if a
default key TTL was set using ith the -L to dnssec-keygen. If
either of those is true, this option may still be used; it will
override the values found in the zone file or the key file.
If this option is not used and the key TTL cannot be retrieved from
the zone file or the key file, then a warning is generated and a
default value of 1 day is used.
-rresign interval
Sets the value to be used as the resign interval for the zone or
zones being analyzed when determining whether there is a possibility
of validation failure. This value defaults to 22.5 days, which is
also the default in named. However, if it has been changed by the
sig-validity-interval option in named.conf, then it should also
be changed here.
The length of the interval can be set in seconds, or in larger units
of time by adding a suffix: mi for minutes, h for hours, d for days,
w for weeks, mo for months, y for years.
-k
Only check KSK coverage; ignore ZSK events. Cannot be used with
-z.
-z
Only check ZSK coverage; ignore KSK events. Cannot be used with
-k.
-ccompilezone path
Specifies a path to a named-compilezone binary. Used for testing.
dnssec-keymgr is a high level Python wrapper to facilitate the key
rollover process for zones handled by BIND. It uses the BIND commands
for manipulating DNSSEC key metadata: dnssec-keygen and
dnssec-settime.
DNSSEC policy can be read from a configuration file (default
/etc/dnssec-policy.conf), from which the key parameters, publication and
rollover schedule, and desired coverage duration for any given zone can
be determined. This file may be used to define individual DNSSEC
policies on a per-zone basis, or to set a “default” policy used for all
zones.
When dnssec-keymgr runs, it examines the DNSSEC keys for one or more
zones, comparing their timing metadata against the policies for those
zones. If key settings do not conform to the DNSSEC policy (for example,
because the policy has been changed), they are automatically corrected.
A zone policy can specify a duration for which we want to ensure the key
correctness (coverage). It can also specify a rollover period
(roll-period). If policy indicates that a key should roll over
before the coverage period ends, then a successor key will automatically
be created and added to the end of the key series.
If zones are specified on the command line, dnssec-keymgr will
examine only those zones. If a specified zone does not already have keys
in place, then keys will be generated for it according to policy.
If zones are not specified on the command line, then dnssec-keymgr
will search the key directory (either the current working directory or
the directory set by the -K option), and check the keys for all the
zones represented in the directory.
Key times that are in the past will not be updated unless the -f is
used (see below). Key inactivation and deletion times that are less than
five minutes in the future will be delayed by five minutes.
It is expected that this tool will be run automatically and unattended
(for example, by cron).
If -c is specified, then the DNSSEC policy is read from file.
(If not specified, then the policy is read from
/etc/dnssec-policy.conf; if that file doesnt exist, a built-in global
default policy is used.)
-f
Force: allow updating of key events even if they are already in the
past. This is not recommended for use with zones in which keys have
already been published. However, if a set of keys has been generated
all of which have publication and activation dates in the past, but
the keys have not been published in a zone as yet, then this option
can be used to clean them up and turn them into a proper series of
keys with appropriate rollover intervals.
-gkeygen-path
Specifies a path to a dnssec-keygen binary. Used for testing. See
also the -s option.
-h
Print the dnssec-keymgr help summary and exit.
-Kdirectory
Sets the directory in which keys can be found. Defaults to the
current working directory.
-k
Only apply policies to KSK keys. See also the -z option.
-q
Quiet: suppress printing of dnssec-keygen and dnssec-settime.
-ssettime-path
Specifies a path to a dnssec-settime binary. Used for testing.
See also the -g option.
-v
Print the dnssec-keymgr version and exit.
-z
Only apply policies to ZSK keys. See also the -k option.
The dnssec-policy.conf file can specify three kinds of policies:
· Policy classes (policyname{...};) can be
inherited by zone policies or other policy classes; these can be used
to create sets of different security profiles. For example, a policy
class normal might specify 1024-bit key sizes, but a class
extra might specify 2048 bits instead; extra would be used
for zones that had unusually high security needs.
· Algorithm policies: (algorithm-policyalgorithm{...}; ) override default per-algorithm settings. For example, by
default, RSASHA256 keys use 2048-bit key sizes for both KSK and ZSK.
This can be modified using algorithm-policy, and the new key
sizes would then be used for any key of type RSASHA256.
· Zone policies: (zonename{...}; ) set policy for a
single zone by name. A zone policy can inherit a policy class by
including a policy option. Zone names beginning with digits
(i.e., 0-9) must be quoted. If a zone does not have its own policy
then the “default” policy applies.
Options that can be specified in policies:
algorithmname;
The key algorithm. If no policy is defined, the default is RSASHA256.
coverageduration;
The length of time to ensure that keys will be correct; no action
will be taken to create new keys to be activated after this time.
This can be represented as a number of seconds, or as a duration
using human-readable units (examples: “1y” or “6 months”). A default
value for this option can be set in algorithm policies as well as in
policy classes or zone policies. If no policy is configured, the
default is six months.
directorypath;
Specifies the directory in which keys should be stored.
key-sizekeytypesize;
Specifies the number of bits to use in creating keys. The keytype is
either “zsk” or “ksk”. A default value for this option can be set in
algorithm policies as well as in policy classes or zone policies. If
no policy is configured, the default is 2048 bits for RSA keys.
keyttlduration;
The key TTL. If no policy is defined, the default is one hour.
post-publishkeytypeduration;
How long after inactivation a key should be deleted from the zone.
Note: If roll-period is not set, this value is ignored. The
keytype is either “zsk” or “ksk”. A default duration for this option
can be set in algorithm policies as well as in policy classes or zone
policies. The default is one month.
pre-publishkeytypeduration;
How long before activation a key should be published. Note: If
roll-period is not set, this value is ignored. The keytype is
either “zsk” or “ksk”. A default duration for this option can be set
in algorithm policies as well as in policy classes or zone policies.
The default is one month.
roll-periodkeytypeduration;
How frequently keys should be rolled over. The keytype is either
“zsk” or “ksk”. A default duration for this option can be set in
algorithm policies as well as in policy classes or zone policies. If
no policy is configured, the default is one year for ZSKs. KSKs do
not roll over by default.
· Enable scheduling of KSK rollovers using the -Psync and -Dsync options to dnssec-keygen and dnssec-settime. Check the
parent zone (as in dnssec-checkds) to determine when its safe for
the key to roll.
· Allow configuration of standby keys and use of the REVOKE bit, for
keys that use RFC 5011 semantics.
dnssec-keyfromlabel generates a pair of key files that reference a
key object stored in a cryptographic hardware service module (HSM). The
private key file can be used for DNSSEC signing of zone data as if it
were a conventional signing key created by dnssec-keygen, but the
key material is stored within the HSM and the actual signing takes
place there.
The name of the key is specified on the command line. This must
match the name of the zone for which the key is being generated.
This option selects the cryptographic algorithm. The value of algorithm must
be one of RSASHA1, NSEC3RSASHA1, RSASHA256, RSASHA512,
ECDSAP256SHA256, ECDSAP384SHA384, ED25519, or ED448.
These values are case-insensitive. In some cases, abbreviations are
supported, such as ECDSA256 for ECDSAP256SHA256 and ECDSA384 for
ECDSAP384SHA384. If RSASHA1 is specified along with the -3
option, then NSEC3RSASHA1 is used instead.
This option is mandatory except when using the
-S option, which copies the algorithm from the predecessory key.
Changed in version 9.12.0: The default value RSASHA1 for newly generated keys was removed.
-3
This option uses an NSEC3-capable algorithm to generate a DNSSEC key. If this
option is used with an algorithm that has both NSEC and NSEC3
versions, then the NSEC3 version is used; for example,
dnssec-keygen-3aRSASHA1 specifies the NSEC3RSASHA1 algorithm.
-Eengine
This option specifies the cryptographic hardware to use.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-llabel
This option specifies the label for a key pair in the crypto hardware.
When BIND 9 is built with OpenSSL-based PKCS#11 support, the label is
an arbitrary string that identifies a particular key. It may be
preceded by an optional OpenSSL engine name, followed by a colon, as
in pkcs11:keylabel.
When BIND 9 is built with native PKCS#11 support, the label is a
PKCS#11 URI string in the format
pkcs11:keyword\=value[;\keyword\=value;...]. Keywords
include token, which identifies the HSM; object, which identifies
the key; and pin-source, which identifies a file from which the
HSM’s PIN code can be obtained. The label is stored in the
on-disk private file.
If the label contains a pin-source field, tools using the
generated key files are able to use the HSM for signing and other
operations without any need for an operator to manually enter a PIN.
Note: Making the HSM’s PIN accessible in this manner may reduce the
security advantage of using an HSM; use caution
with this feature.
-nnametype
This option specifies the owner type of the key. The value of nametype must
either be ZONE (for a DNSSEC zone key (KEY/DNSKEY)), HOST or ENTITY
(for a key associated with a host (KEY)), USER (for a key associated
with a user (KEY)), or OTHER (DNSKEY). These values are
case-insensitive.
-C
This option enables compatibility mode, which generates an old-style key, without any metadata.
By default, dnssec-keyfromlabel includes the key’s creation
date in the metadata stored with the private key; other dates may
be set there as well, including publication date, activation date, etc. Keys
that include this data may be incompatible with older versions of
BIND; the -C option suppresses them.
-cclass
This option indicates that the DNS record containing the key should have the
specified class. If not specified, class IN is used.
-fflag
This option sets the specified flag in the flag field of the KEY/DNSKEY record.
The only recognized flags are KSK (Key-Signing Key) and REVOKE.
-G
This option generates a key, but does not publish it or sign with it. This option is
incompatible with -P and -A.
-h
This option prints a short summary of the options and arguments to
dnssec-keyfromlabel.
-Kdirectory
This option sets the directory in which the key files are to be written.
-k
This option generates KEY records rather than DNSKEY records.
-L ttl
This option sets the default TTL to use for this key when it is converted into a
DNSKEY RR. This is the TTL used when the key is imported into a zone,
unless there was already a DNSKEY RRset in
place, in which case the existing TTL would take precedence. Setting
the default TTL to 0 or none removes it.
-pprotocol
This option sets the protocol value for the key. The protocol is a number between
0 and 255. The default is 3 (DNSSEC). Other possible values for this
argument are listed in RFC 2535 and its successors.
-Skey
This option generates a key as an explicit successor to an existing key. The name,
algorithm, size, and type of the key are set to match the
predecessor. The activation date of the new key is set to the
inactivation date of the existing one. The publication date is
set to the activation date minus the prepublication interval, which
defaults to 30 days.
-ttype
This option indicates the type of the key. type must be one of AUTHCONF,
NOAUTHCONF, NOAUTH, or NOCONF. The default is AUTHCONF. AUTH refers
to the ability to authenticate data, and CONF to the ability to encrypt
data.
-vlevel
This option sets the debugging level.
-V
This option prints version information.
-y
This option allows DNSSEC key files to be generated even if the key ID would
collide with that of an existing key, in the event of either key
being revoked. (This is only safe to enable if
RFC 5011 trust anchor maintenance is not used with either of the keys
involved.)
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS. If the
argument begins with a + or -, it is interpreted as an offset from
the present time. For convenience, if such an offset is followed by one
of the suffixes y, mo, w, d, h, or mi, then the offset is
computed in years (defined as 365 24-hour days, ignoring leap years),
months (defined as 30 24-hour days), weeks, days, hours, or minutes,
respectively. Without a suffix, the offset is computed in seconds. To
explicitly prevent a date from being set, use none or never.
-Pdate/offset
This option sets the date on which a key is to be published to the zone. After
that date, the key is included in the zone but is not used
to sign it. If not set, and if the -G option has not been used, the
default is the current date.
-Psyncdate/offset
This option sets the date on which CDS and CDNSKEY records that match this key
are to be published to the zone.
-Adate/offset
This option sets the date on which the key is to be activated. After that date,
the key is included in the zone and used to sign it. If not set,
and if the -G option has not been used, the default is the current date.
-Rdate/offset
This option sets the date on which the key is to be revoked. After that date, the
key is flagged as revoked. It is included in the zone and
is used to sign it.
-Idate/offset
This option sets the date on which the key is to be retired. After that date, the
key is still included in the zone, but it is not used to
sign it.
-Ddate/offset
This option sets the date on which the key is to be deleted. After that date, the
key is no longer included in the zone. (However, it may remain in the key
repository.)
-Dsyncdate/offset
This option sets the date on which the CDS and CDNSKEY records that match this
key are to be deleted.
-iinterval
This option sets the prepublication interval for a key. If set, then the
publication and activation dates must be separated by at least this
much time. If the activation date is specified but the publication
date is not, the publication date defaults to this much time
before the activation date; conversely, if the publication date is
specified but not the activation date, activation is set to
this much time after publication.
If the key is being created as an explicit successor to another key,
then the default prepublication interval is 30 days; otherwise it is
zero.
As with date offsets, if the argument is followed by one of the
suffixes y, mo, w, d, h, or mi, the interval is
measured in years, months, weeks, days, hours, or minutes,
respectively. Without a suffix, the interval is measured in seconds.
When dnssec-keyfromlabel completes successfully, it prints a string
of the form Knnnn.+aaa+iiiii to the standard output. This is an
identification string for the key files it has generated.
nnnn is the key name.
aaa is the numeric representation of the algorithm.
iiiii is the key identifier (or footprint).
dnssec-keyfromlabel creates two files, with names based on the
printed string. Knnnn.+aaa+iiiii.key contains the public key, and
Knnnn.+aaa+iiiii.private contains the private key.
The .key file contains a DNS KEY record that can be inserted into a
zone file (directly or with an $INCLUDE statement).
The .private file contains algorithm-specific fields. For obvious
security reasons, this file does not have general read permission.
dnssec-keygen generates keys for DNSSEC (Secure DNS), as defined in
RFC 2535 and RFC 4034. It can also generate keys for use with TSIG
(Transaction Signatures) as defined in RFC 2845, or TKEY (Transaction
Key) as defined in RFC 2930.
The name of the key is specified on the command line. For DNSSEC
keys, this must match the name of the zone for which the key is being
generated.
The dnssec-keymgr command acts as a wrapper
around dnssec-keygen, generating and updating keys
as needed to enforce defined security policies such as key rollover
scheduling. Using dnssec-keymgr may be preferable
to direct use of dnssec-keygen.
This option uses an NSEC3-capable algorithm to generate a DNSSEC key. If this
option is used with an algorithm that has both NSEC and NSEC3
versions, then the NSEC3 version is selected; for example,
dnssec-keygen-3-aRSASHA1 specifies the NSEC3RSASHA1 algorithm.
-aalgorithm
This option selects the cryptographic algorithm. For DNSSEC keys, the value of
algorithm must be one of RSASHA1, NSEC3RSASHA1, RSASHA256,
RSASHA512, ECDSAP256SHA256, ECDSAP384SHA384, ED25519, or ED448. For
TKEY, the value must be DH (Diffie-Hellman); specifying this value
automatically sets the -TKEY option as well.
These values are case-insensitive. In some cases, abbreviations are
supported, such as ECDSA256 for ECDSAP256SHA256 and ECDSA384 for
ECDSAP384SHA384. If RSASHA1 is specified along with the -3
option, NSEC3RSASHA1 is used instead.
This parameter must be specified except when using the -S
option, which copies the algorithm from the predecessor key.
In prior releases, HMAC algorithms could be generated for use as TSIG
keys, but that feature was removed in BIND 9.13.0. Use
tsig-keygen to generate TSIG keys.
-bkeysize
This option specifies the number of bits in the key. The choice of key size
depends on the algorithm used: RSA keys must be between 1024 and 4096
bits; Diffie-Hellman keys must be between 128 and 4096 bits. Elliptic
curve algorithms do not need this parameter.
If the key size is not specified, some algorithms have pre-defined
defaults. For example, RSA keys for use as DNSSEC zone-signing keys
have a default size of 1024 bits; RSA keys for use as key-signing
keys (KSKs, generated with -fKSK) default to 2048 bits.
-C
This option enables compatibility mode, which generates an old-style key, without any timing
metadata. By default, dnssec-keygen includes the key’s
creation date in the metadata stored with the private key; other
dates may be set there as well, including publication date, activation date,
etc. Keys that include this data may be incompatible with older
versions of BIND; the -C option suppresses them.
-cclass
This option indicates that the DNS record containing the key should have the
specified class. If not specified, class IN is used.
-dbits
This option specifies the key size in bits. For the algorithms RSASHA1, NSEC3RSASA1, RSASHA256, and
RSASHA512 the key size must be between 1024 and 4096 bits; DH size is between 128
and 4096 bits. This option is ignored for algorithms ECDSAP256SHA256,
ECDSAP384SHA384, ED25519, and ED448.
-Eengine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-fflag
This option sets the specified flag in the flag field of the KEY/DNSKEY record.
The only recognized flags are KSK (Key-Signing Key) and REVOKE.
-G
This option generates a key, but does not publish it or sign with it. This option is
incompatible with -P and -A.
-ggenerator
This option indicates the generator to use if generating a Diffie-Hellman key. Allowed
values are 2 and 5. If no generator is specified, a known prime from
RFC 2539 is used if possible; otherwise the default is 2.
-h
This option prints a short summary of the options and arguments to
dnssec-keygen.
-Kdirectory
This option sets the directory in which the key files are to be written.
-kpolicy
This option creates keys for a specific dnssec-policy. If a policy uses multiple keys,
dnssec-keygen generates multiple keys. This also
creates a “.state” file to keep track of the key state.
This option creates keys according to the dnssec-policy configuration, hence
it cannot be used at the same time as many of the other options that
dnssec-keygen provides.
-Lttl
This option sets the default TTL to use for this key when it is converted into a
DNSKEY RR. This is the TTL used when the key is imported into a zone,
unless there was already a DNSKEY RRset in
place, in which case the existing TTL takes precedence. If this
value is not set and there is no existing DNSKEY RRset, the TTL
defaults to the SOA TTL. Setting the default TTL to 0 or none
is the same as leaving it unset.
-lfile
This option provides a configuration file that contains a dnssec-policy statement
(matching the policy set with -k).
-nnametype
This option specifies the owner type of the key. The value of nametype must
either be ZONE (for a DNSSEC zone key (KEY/DNSKEY)), HOST or ENTITY
(for a key associated with a host (KEY)), USER (for a key associated
with a user (KEY)), or OTHER (DNSKEY). These values are
case-insensitive. The default is ZONE for DNSKEY generation.
-pprotocol
This option sets the protocol value for the generated key, for use with
-TKEY. The protocol is a number between 0 and 255. The default
is 3 (DNSSEC). Other possible values for this argument are listed in
RFC 2535 and its successors.
-q
This option sets quiet mode, which suppresses unnecessary output, including progress
indication. Without this option, when dnssec-keygen is run
interactively to generate an RSA or DSA key pair, it prints a
string of symbols to stderr indicating the progress of the key
generation. A . indicates that a random number has been found which
passed an initial sieve test; + means a number has passed a single
round of the Miller-Rabin primality test; and a space ( ) means that the
number has passed all the tests and is a satisfactory key.
-Skey
This option creates a new key which is an explicit successor to an existing key.
The name, algorithm, size, and type of the key are set to match
the existing key. The activation date of the new key is set to
the inactivation date of the existing one. The publication date is
set to the activation date minus the prepublication interval,
which defaults to 30 days.
-sstrength
This option specifies the strength value of the key. The strength is a number
between 0 and 15, and currently has no defined purpose in DNSSEC.
-Trrtype
This option specifies the resource record type to use for the key. rrtype
must be either DNSKEY or KEY. The default is DNSKEY when using a
DNSSEC algorithm, but it can be overridden to KEY for use with
SIG(0).
-ttype
This option indicates the type of the key for use with -TKEY. type
must be one of AUTHCONF, NOAUTHCONF, NOAUTH, or NOCONF. The default
is AUTHCONF. AUTH refers to the ability to authenticate data, and
CONF to the ability to encrypt data.
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS. If the
argument begins with a + or -, it is interpreted as an offset from
the present time. For convenience, if such an offset is followed by one
of the suffixes y, mo, w, d, h, or mi, then the offset is
computed in years (defined as 365 24-hour days, ignoring leap years),
months (defined as 30 24-hour days), weeks, days, hours, or minutes,
respectively. Without a suffix, the offset is computed in seconds. To
explicitly prevent a date from being set, use none or never.
-Pdate/offset
This option sets the date on which a key is to be published to the zone. After
that date, the key is included in the zone but is not used
to sign it. If not set, and if the -G option has not been used, the
default is the current date.
-Psyncdate/offset
This option sets the date on which CDS and CDNSKEY records that match this key
are to be published to the zone.
-Adate/offset
This option sets the date on which the key is to be activated. After that date,
the key is included in the zone and used to sign it. If not set,
and if the -G option has not been used, the default is the current date. If set,
and -P is not set, the publication date is set to the
activation date minus the prepublication interval.
-Rdate/offset
This option sets the date on which the key is to be revoked. After that date, the
key is flagged as revoked. It is included in the zone and
is used to sign it.
-Idate/offset
This option sets the date on which the key is to be retired. After that date, the
key is still included in the zone, but it is not used to
sign it.
-Ddate/offset
This option sets the date on which the key is to be deleted. After that date, the
key is no longer included in the zone. (However, it may remain in the key
repository.)
-Dsyncdate/offset
This option sets the date on which the CDS and CDNSKEY records that match this
key are to be deleted.
-iinterval
This option sets the prepublication interval for a key. If set, then the
publication and activation dates must be separated by at least this
much time. If the activation date is specified but the publication
date is not, the publication date defaults to this much time
before the activation date; conversely, if the publication date is
specified but not the activation date, activation is set to
this much time after publication.
If the key is being created as an explicit successor to another key,
then the default prepublication interval is 30 days; otherwise it is
zero.
As with date offsets, if the argument is followed by one of the
suffixes y, mo, w, d, h, or mi, the interval is
measured in years, months, weeks, days, hours, or minutes,
respectively. Without a suffix, the interval is measured in seconds.
When dnssec-keygen completes successfully, it prints a string of the
form Knnnn.+aaa+iiiii to the standard output. This is an
identification string for the key it has generated.
nnnn is the key name.
aaa is the numeric representation of the algorithm.
iiiii is the key identifier (or footprint).
dnssec-keygen creates two files, with names based on the printed
string. Knnnn.+aaa+iiiii.key contains the public key, and
Knnnn.+aaa+iiiii.private contains the private key.
The .key file contains a DNSKEY or KEY record. When a zone is being
signed by named or dnssec-signzone-S, DNSKEY records are
included automatically. In other cases, the .key file can be
inserted into a zone file manually or with an $INCLUDE statement.
The .private file contains algorithm-specific fields. For obvious
security reasons, this file does not have general read permission.
dnssec-revoke reads a DNSSEC key file, sets the REVOKED bit on the
key as defined in RFC 5011, and creates a new pair of key files
containing the now-revoked key.
This option sets the directory in which the key files are to reside.
-r
This option indicates to remove the original keyset files after writing the new keyset files.
-vlevel
This option sets the debugging level.
-V
This option prints version information.
-Eengine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-f
This option indicates a forced overwrite and causes dnssec-revoke to write the new key pair,
even if a file already exists matching the algorithm and key ID of
the revoked key.
-R
This option prints the key tag of the key with the REVOKE bit set, but does not
revoke the key.
dnssec-settime reads a DNSSEC private key file and sets the key
timing metadata as specified by the -P, -A, -R, -I, and
-D options. The metadata can then be used by dnssec-signzone or
other signing software to determine when a key is to be published,
whether it should be used for signing a zone, etc.
If none of these options is set on the command line,
dnssec-settime simply prints the key timing metadata already stored
in the key.
When key metadata fields are changed, both files of a key pair
(Knnnn.+aaa+iiiii.key and Knnnn.+aaa+iiiii.private) are
regenerated.
Metadata fields are stored in the private file. A
human-readable description of the metadata is also placed in comments in
the key file. The private file’s permissions are always set to be
inaccessible to anyone other than the owner (mode 0600).
When working with state files, it is possible to update the timing metadata in
those files as well with -s. With this option, it is also possible to update key
states with -d (DS), -k (DNSKEY), -r (RRSIG of KSK), or -z
(RRSIG of ZSK). Allowed states are HIDDEN, RUMOURED, OMNIPRESENT, and
UNRETENTIVE.
The goal state of the key can also be set with -g. This should be either
HIDDEN or OMNIPRESENT, representing whether the key should be removed from the
zone or published.
It is NOT RECOMMENDED to manipulate state files manually, except for testing
purposes.
This option forces an update of an old-format key with no metadata fields. Without
this option, dnssec-settime fails when attempting to update a
legacy key. With this option, the key is recreated in the new
format, but with the original key data retained. The key’s creation
date is set to the present time. If no other values are
specified, then the key’s publication and activation dates are also
set to the present time.
-Kdirectory
This option sets the directory in which the key files are to reside.
-Lttl
This option sets the default TTL to use for this key when it is converted into a
DNSKEY RR. This is the TTL used when the key is imported into a zone,
unless there was already a DNSKEY RRset in
place, in which case the existing TTL takes precedence. If this
value is not set and there is no existing DNSKEY RRset, the TTL
defaults to the SOA TTL. Setting the default TTL to 0 or none
removes it from the key.
-h
This option emits a usage message and exits.
-V
This option prints version information.
-vlevel
This option sets the debugging level.
-Eengine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS. If the
argument begins with a + or -, it is interpreted as an offset from
the present time. For convenience, if such an offset is followed by one
of the suffixes y, mo, w, d, h, or mi, then the offset is
computed in years (defined as 365 24-hour days, ignoring leap years),
months (defined as 30 24-hour days), weeks, days, hours, or minutes,
respectively. Without a suffix, the offset is computed in seconds. To
explicitly prevent a date from being set, use none or never.
-Pdate/offset
This option sets the date on which a key is to be published to the zone. After
that date, the key is included in the zone but is not used
to sign it.
-Pdsdate/offset
This option Sets the date on which DS records that match this key have been
seen in the parent zone.
-Psyncdate/offset
This option sets the date on which CDS and CDNSKEY records that match this key
are to be published to the zone.
-Adate/offset
This option sets the date on which the key is to be activated. After that date,
the key is included in the zone and used to sign it.
-Rdate/offset
This option sets the date on which the key is to be revoked. After that date, the
key is flagged as revoked. It is included in the zone and
is used to sign it.
-Idate/offset
This option sets the date on which the key is to be retired. After that date, the
key is still included in the zone, but it is not used to
sign it.
-Ddate/offset
This option sets the date on which the key is to be deleted. After that date, the
key is no longer included in the zone. (However, it may remain in the key
repository.)
-Ddsdate/offset
This option sets the date on which the DS records that match this key have
been seen removed from the parent zone.
-Dsyncdate/offset
This option sets the date on which the CDS and CDNSKEY records that match this
key are to be deleted.
-Spredecessorkey
This option selects a key for which the key being modified is an explicit
successor. The name, algorithm, size, and type of the predecessor key
must exactly match those of the key being modified. The activation
date of the successor key is set to the inactivation date of the
predecessor. The publication date is set to the activation date
minus the prepublication interval, which defaults to 30 days.
-iinterval
This option sets the prepublication interval for a key. If set, then the
publication and activation dates must be separated by at least this
much time. If the activation date is specified but the publication
date is not, the publication date defaults to this much time
before the activation date; conversely, if the publication date is
specified but not the activation date, activation is set to
this much time after publication.
If the key is being created as an explicit successor to another key,
then the default prepublication interval is 30 days; otherwise it is
zero.
As with date offsets, if the argument is followed by one of the
suffixes y, mo, w, d, h, or mi, the interval is
measured in years, months, weeks, days, hours, or minutes,
respectively. Without a suffix, the interval is measured in seconds.
To test dnssec-policy it may be necessary to construct keys with artificial
state information; these options are used by the testing framework for that
purpose, but should never be used in production.
Known key states are HIDDEN, RUMOURED, OMNIPRESENT, and UNRETENTIVE.
-s
This option indicates that when setting key timing data, the state file should also be updated.
-gstate
This option sets the goal state for this key. Must be HIDDEN or OMNIPRESENT.
-dstatedate/offset
This option sets the DS state for this key as of the specified date, offset from the current date.
-kstatedate/offset
This option sets the DNSKEY state for this key as of the specified date, offset from the current date.
-rstatedate/offset
This option sets the RRSIG (KSK) state for this key as of the specified date, offset from the current date.
-zstatedate/offset
This option sets the RRSIG (ZSK) state for this key as of the specified date, offset from the current date.
dnssec-settime can also be used to print the timing metadata
associated with a key.
-u
This option indicates that times should be printed in Unix epoch format.
-pC/P/Pds/Psync/A/R/I/D/Dds/Dsync/all
This option prints a specific metadata value or set of metadata values.
The -p option may be followed by one or more of the following letters or
strings to indicate which value or values to print: C for the
creation date, P for the publication date, Pds`fortheDSpublicationdate,``Psync for the CDS and CDNSKEY publication date, A for the
activation date, R for the revocation date, I for the inactivation
date, D for the deletion date, Dds for the DS deletion date,
and Dsync for the CDS and CDNSKEY deletion date. To print all of the
metadata, use all.
dnssec-signzone signs a zone; it generates NSEC and RRSIG records
and produces a signed version of the zone. The security status of
delegations from the signed zone (that is, whether the child zones are
secure) is determined by the presence or absence of a keyset
file for each child zone.
This option sets compatibility mode, in which a keyset-zonename file is generated in addition
to dsset-zonename when signing a zone, for use by older versions
of dnssec-signzone.
-ddirectory
This option indicates the directory where BIND 9 should look for dsset- or keyset- files.
-D
This option indicates that only those record types automatically managed by
dnssec-signzone, i.e., RRSIG, NSEC, NSEC3 and NSEC3PARAM records, should be included in the output.
If smart signing (-S) is used, DNSKEY records are also included.
The resulting file can be included in the original zone file with
$INCLUDE. This option cannot be combined with -Oraw,
-Omap, or serial-number updating.
-Eengine
This option specifies the hardware to use for cryptographic
operations, such as a secure key store used for signing, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-g
This option indicates that DS records for child zones should be generated from a dsset- or keyset-
file. Existing DS records are removed.
-Kdirectory
This option specifies the directory to search for DNSSEC keys. If not
specified, it defaults to the current directory.
-kkey
This option tells BIND 9 to treat the specified key as a key-signing key, ignoring any key flags. This
option may be specified multiple times.
-Mmaxttl
This option sets the maximum TTL for the signed zone. Any TTL higher than maxttl
in the input zone is reduced to maxttl in the output. This
provides certainty as to the largest possible TTL in the signed zone,
which is useful to know when rolling keys. The maxttl is the longest
possible time before signatures that have been retrieved by resolvers
expire from resolver caches. Zones that are signed with this
option should be configured to use a matching max-zone-ttl in
named.conf. (Note: This option is incompatible with -D,
because it modifies non-DNSSEC data in the output zone.)
-sstart-time
This option specifies the date and time when the generated RRSIG records become
valid. This can be either an absolute or relative time. An absolute
start time is indicated by a number in YYYYMMDDHHMMSS notation;
20000530144500 denotes 14:45:00 UTC on May 30th, 2000. A relative
start time is indicated by +N, which is N seconds from the current
time. If no start-time is specified, the current time minus 1
hour (to allow for clock skew) is used.
-eend-time
This option specifies the date and time when the generated RRSIG records expire. As
with start-time, an absolute time is indicated in YYYYMMDDHHMMSS
notation. A time relative to the start time is indicated with +N,
which is N seconds from the start time. A time relative to the
current time is indicated with now+N. If no end-time is
specified, 30 days from the start time is the default.
end-time must be later than start-time.
-Xextendedend-time
This option specifies the date and time when the generated RRSIG records for the
DNSKEY RRset expire. This is to be used in cases when the DNSKEY
signatures need to persist longer than signatures on other records;
e.g., when the private component of the KSK is kept offline and the
KSK signature is to be refreshed manually.
As with end-time, an absolute time is indicated in
YYYYMMDDHHMMSS notation. A time relative to the start time is
indicated with +N, which is N seconds from the start time. A time
relative to the current time is indicated with now+N. If no
extendedend-time is specified, the value of end-time is used
as the default. (end-time, in turn, defaults to 30 days from the
start time.) extendedend-time must be later than start-time.
-foutput-file
This option indicates the name of the output file containing the signed zone. The default
is to append .signed to the input filename. If output-file is
set to -, then the signed zone is written to the standard
output, with a default output format of full.
-h
This option prints a short summary of the options and arguments to
dnssec-signzone.
-V
This option prints version information.
-iinterval
This option indicates that, when a previously signed zone is passed as input, records may be
re-signed. The interval option specifies the cycle interval as an
offset from the current time, in seconds. If a RRSIG record expires
after the cycle interval, it is retained; otherwise, it is considered
to be expiring soon and it is replaced.
The default cycle interval is one quarter of the difference between
the signature end and start times. So if neither end-time nor
start-time is specified, dnssec-signzone generates
signatures that are valid for 30 days, with a cycle interval of 7.5
days. Therefore, if any existing RRSIG records are due to expire in
less than 7.5 days, they are replaced.
-Iinput-format
This option sets the format of the input zone file. Possible formats are text
(the default), raw, and map. This option is primarily
intended to be used for dynamic signed zones, so that the dumped zone
file in a non-text format containing updates can be signed directly.
This option is not useful for non-dynamic zones.
-jjitter
When signing a zone with a fixed signature lifetime, all RRSIG
records issued at the time of signing expire simultaneously. If the
zone is incrementally signed, i.e., a previously signed zone is passed
as input to the signer, all expired signatures must be regenerated
at approximately the same time. The jitter option specifies a jitter
window that is used to randomize the signature expire time, thus
spreading incremental signature regeneration over time.
Signature lifetime jitter also, to some extent, benefits validators and
servers by spreading out cache expiration, i.e., if large numbers of
RRSIGs do not expire at the same time from all caches, there is
less congestion than if all validators need to refetch at around the
same time.
-Lserial
When writing a signed zone to “raw” or “map” format, this option sets the “source
serial” value in the header to the specified serial number. (This is
expected to be used primarily for testing purposes.)
-nncpus
This option specifies the number of threads to use. By default, one thread is
started for each detected CPU.
-Nsoa-serial-format
This option sets the SOA serial number format of the signed zone. Possible formats are
keep (the default), increment, unixtime, and
date.
keep
This format indicates that the SOA serial number should not be modified.
increment
This format increments the SOA serial number using RFC 1982 arithmetic.
unixtime
This format sets the SOA serial number to the number of seconds
since the beginning of the Unix epoch, unless the serial
number is already greater than or equal to that value, in
which case it is simply incremented by one.
date
This format sets the SOA serial number to today’s date, in
YYYYMMDDNN format, unless the serial number is already greater
than or equal to that value, in which case it is simply
incremented by one.
-oorigin
This option sets the zone origin. If not specified, the name of the zone file is
assumed to be the origin.
-Ooutput-format
This option sets the format of the output file containing the signed zone. Possible
formats are text (the default), which is the standard textual
representation of the zone; full, which is text output in a
format suitable for processing by external scripts; and map,
raw, and raw=N, which store the zone in binary formats
for rapid loading by named. raw=N specifies the format
version of the raw zone file: if N is 0, the raw file can be read by
any version of named; if N is 1, the file can be read by release
9.9.0 or higher. The default is 1.
-P
This option disables post-sign verification tests.
The post-sign verification tests ensure that for each algorithm in
use there is at least one non-revoked self-signed KSK key, that all
revoked KSK keys are self-signed, and that all records in the zone
are signed by the algorithm. This option skips these tests.
-Q
This option removes signatures from keys that are no longer active.
Normally, when a previously signed zone is passed as input to the
signer, and a DNSKEY record has been removed and replaced with a new
one, signatures from the old key that are still within their validity
period are retained. This allows the zone to continue to validate
with cached copies of the old DNSKEY RRset. The -Q option forces
dnssec-signzone to remove signatures from keys that are no longer
active. This enables ZSK rollover using the procedure described in
RFC 4641#4.2.1.1 (“Pre-Publish Key Rollover”).
-q
This option enables quiet mode, which suppresses unnecessary output. Without this option, when
dnssec-signzone is run it prints three pieces of information to standard output: the number of
keys in use; the algorithms used to verify the zone was signed correctly and
other status information; and the filename containing the signed
zone. With the option that output is suppressed, leaving only the filename.
-R
This option removes signatures from keys that are no longer published.
This option is similar to -Q, except it forces
dnssec-signzone to remove signatures from keys that are no longer
published. This enables ZSK rollover using the procedure described in
RFC 4641#4.2.1.2 (“Double Signature Zone Signing Key
Rollover”).
-S
This option enables smart signing, which instructs dnssec-signzone to search the key
repository for keys that match the zone being signed, and to include
them in the zone if appropriate.
When a key is found, its timing metadata is examined to determine how
it should be used, according to the following rules. Each successive
rule takes priority over the prior ones:
If no timing metadata has been set for the key, the key is
published in the zone and used to sign the zone.
If the key’s publication date is set and is in the past, the key
is published in the zone.
If the key’s activation date is set and is in the past, the key is
published (regardless of publication date) and used to sign the
zone.
If the key’s revocation date is set and is in the past, and the key
is published, then the key is revoked, and the revoked key is used
to sign the zone.
If either the key’s unpublication or deletion date is set and
in the past, the key is NOT published or used to sign the zone,
regardless of any other metadata.
If the key’s sync publication date is set and is in the past,
synchronization records (type CDS and/or CDNSKEY) are created.
If the key’s sync deletion date is set and is in the past,
synchronization records (type CDS and/or CDNSKEY) are removed.
-Tttl
This option specifies a TTL to be used for new DNSKEY records imported into the
zone from the key repository. If not specified, the default is the
TTL value from the zone’s SOA record. This option is ignored when
signing without -S, since DNSKEY records are not imported from
the key repository in that case. It is also ignored if there are any
pre-existing DNSKEY records at the zone apex, in which case new
records’ TTL values are set to match them, or if any of the
imported DNSKEY records had a default TTL value. In the event of a
conflict between TTL values in imported keys, the shortest one is
used.
-t
This option prints statistics at completion.
-u
This option updates the NSEC/NSEC3 chain when re-signing a previously signed zone.
With this option, a zone signed with NSEC can be switched to NSEC3,
or a zone signed with NSEC3 can be switched to NSEC or to NSEC3 with
different parameters. Without this option, dnssec-signzone
retains the existing chain when re-signing.
-vlevel
This option sets the debugging level.
-x
This option indicates that BIND 9 should only sign the DNSKEY, CDNSKEY, and CDS RRsets with key-signing keys,
and should omit signatures from zone-signing keys. (This is similar to the
dnssec-dnskey-kskonlyyes; zone option in named.)
-z
This option indicates that BIND 9 should ignore the KSK flag on keys when determining what to sign. This causes
KSK-flagged keys to sign all records, not just the DNSKEY RRset.
(This is similar to the update-check-kskno; zone option in
named.)
-3salt
This option generates an NSEC3 chain with the given hex-encoded salt. A dash
(-) can be used to indicate that no salt is to be used when
generating the NSEC3 chain.
Note
-3- is the recommended configuration. Adding salt provides no practical benefits.
-Hiterations
This option indicates that, when generating an NSEC3 chain, BIND 9 should use this many iterations. The default
is 10.
Warning
Values greater than 0 cause interoperability issues and also increase the risk of CPU-exhausting DoS attacks. The default value has not been changed because the best practices has changed only after BIND 9.16 reached Extended Support Version status.
-A
This option indicates that, when generating an NSEC3 chain, BIND 9 should set the OPTOUT flag on all NSEC3
records and should not generate NSEC3 records for insecure delegations.
Warning
Do not use this option unless all its implications are fully understood. This option is intended only for extremely large zones (comparable to com.) with sparse secure delegations.
Using this option twice (i.e., -AA) turns the OPTOUT flag off for
all records. This is useful when using the -u option to modify an
NSEC3 chain which previously had OPTOUT set.
zonefile
This option sets the file containing the zone to be signed.
key
This option specifies which keys should be used to sign the zone. If no keys are
specified, the zone is examined for DNSKEY records at the
zone apex. If these records are found and there are matching private keys in
the current directory, they are used for signing.
The following command signs the example.com zone with the
ECDSAP256SHA256 key generated by dnssec-keygen
(Kexample.com.+013+17247). Because the -S option is not being used,
the zone’s keys must be in the master file (db.example.com). This
invocation looks for dsset files in the current directory, so that
DS records can be imported from them (-g).
In the above example, dnssec-signzone creates the file
db.example.com.signed. This file should be referenced in a zone
statement in the named.conf file.
This example re-signs a previously signed zone with default parameters.
The private keys are assumed to be in the current directory.
dnssec-verify verifies that a zone is fully signed for each
algorithm found in the DNSKEY RRset for the zone, and that the
NSEC/NSEC3 chains are complete.
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-Iinput-format
This option sets the format of the input zone file. Possible formats are text
(the default) and raw. This option is primarily intended to be used
for dynamic signed zones, so that the dumped zone file in a non-text
format containing updates can be verified independently.
This option is not useful for non-dynamic zones.
-oorigin
This option indicates the zone origin. If not specified, the name of the zone file is
assumed to be the origin.
-vlevel
This option sets the debugging level.
-V
This option prints version information.
-q
This option sets quiet mode, which suppresses output. Without this option, when dnssec-verify
is run it prints to standard output the number of keys in use, the
algorithms used to verify the zone was signed correctly, and other status
information. With this option, all non-error output is suppressed, and only the exit
code indicates success.
-x
This option verifies only that the DNSKEY RRset is signed with key-signing keys.
Without this flag, it is assumed that the DNSKEY RRset is signed
by all active keys. When this flag is set, it is not an error if
the DNSKEY RRset is not signed by zone-signing keys. This corresponds
to the -x option in dnssec-signzone.
-z
This option indicates that the KSK flag on the keys should be ignored when determining whether the zone is
correctly signed. Without this flag, it is assumed that there is
a non-revoked, self-signed DNSKEY with the KSK flag set for each
algorithm, and that RRsets other than DNSKEY RRset are signed with
a different DNSKEY without the KSK flag set.
With this flag set, BIND 9 only requires that for each algorithm, there
be at least one non-revoked, self-signed DNSKEY, regardless of
the KSK flag state, and that other RRsets be signed by a
non-revoked key for the same algorithm that includes the self-signed
key; the same key may be used for both purposes. This corresponds to
the -z option in dnssec-signzone.
zonefile
This option indicates the file containing the zone to be signed.
dnstap-read reads dnstap data from a specified file and prints
it in a human-readable format. By default, dnstap data is printed in
a short summary format, but if the -y option is specified, a
longer and more detailed YAML format is used.
filter-aaaa.so is a query plugin module for named, enabling
named to omit some IPv6 addresses when responding to clients.
Until BIND 9.12, this feature was implemented natively in named and
enabled with the filter-aaaa ACL and the filter-aaaa-on-v4 and
filter-aaaa-on-v6 options. These options are now deprecated in
named.conf but can be passed as parameters to the
filter-aaaa.so plugin, for example:
This module is intended to aid transition from IPv4 to IPv6 by
withholding IPv6 addresses from DNS clients which are not connected to
the IPv6 Internet, when the name being looked up has an IPv4 address
available. Use of this module is not recommended unless absolutely
necessary.
Note: This mechanism can erroneously cause other servers not to give
AAAA records to their clients. If a recursing server with both IPv6 and
IPv4 network connections queries an authoritative server using this
mechanism via IPv4, it is denied AAAA records even if its client is
using IPv6.
This option specifies a list of client addresses for which AAAA filtering is to
be applied. The default is any.
filter-aaaa-on-v4
If set to yes, this option indicates that the DNS client is at an IPv4 address, in
filter-aaaa. If the response does not include DNSSEC
signatures, then all AAAA records are deleted from the response. This
filtering applies to all responses, not only authoritative
ones.
If set to break-dnssec, then AAAA records are deleted even when
DNSSEC is enabled. As suggested by the name, this causes the response
to fail to verify, because the DNSSEC protocol is designed to detect
deletions.
This mechanism can erroneously cause other servers not to give AAAA
records to their clients. If a recursing server with both IPv6 and IPv4
network connections queries an authoritative server using this
mechanism via IPv4, it is denied AAAA records even if its client is
using IPv6.
filter-aaaa-on-v6
This option is identical to filter-aaaa-on-v4, except that it filters AAAA responses
to queries from IPv6 clients instead of IPv4 clients. To filter all
responses, set both options to yes.
host is a simple utility for performing DNS lookups. It is normally
used to convert names to IP addresses and vice versa. When no arguments
or options are given, host prints a short summary of its
command-line arguments and options.
name is the domain name that is to be looked up. It can also be a
dotted-decimal IPv4 address or a colon-delimited IPv6 address, in which
case host by default performs a reverse lookup for that address.
server is an optional argument which is either the name or IP
address of the name server that host should query instead of the
server or servers listed in /etc/resolv.conf.
This option specifies that only IPv4 should be used for query transport. See also the -6 option.
-6
This option specifies that only IPv6 should be used for query transport. See also the -4 option.
-a
The -a (“all”) option is normally equivalent to -v-tANY. It
also affects the behavior of the -l list zone option.
-A
The -A (“almost all”) option is equivalent to -a, except that RRSIG,
NSEC, and NSEC3 records are omitted from the output.
-cclass
This option specifies the query class, which can be used to lookup HS (Hesiod) or CH (Chaosnet)
class resource records. The default class is IN (Internet).
-C
This option indicates that named should check consistency, meaning that host queries the SOA records for zone
name from all the listed authoritative name servers for that
zone. The list of name servers is defined by the NS records that are
found for the zone.
-d
This option prints debugging traces, and is equivalent to the -v verbose option.
-l
This option tells named to list the zone, meaning the host command performs a zone transfer of zone
name and prints out the NS, PTR, and address records (A/AAAA).
Together, the -l-a options print all records in the zone.
-Nndots
This option specifies the number of dots (ndots) that have to be in name for it to be
considered absolute. The default value is that defined using the
ndots statement in /etc/resolv.conf, or 1 if no ndots statement
is present. Names with fewer dots are interpreted as relative names,
and are searched for in the domains listed in the search or
domain directive in /etc/resolv.conf.
-pport
This option specifies the port to query on the server. The default is 53.
-r
This option specifies a non-recursive query; setting this option clears the RD (recursion
desired) bit in the query. This means that the name server
receiving the query does not attempt to resolve name. The -r
option enables host to mimic the behavior of a name server by
making non-recursive queries, and expecting to receive answers to
those queries that can be referrals to other name servers.
-Rnumber
This option specifies the number of retries for UDP queries. If number is negative or zero,
the number of retries is silently set to 1. The default value is 1, or
the value of the attempts option in /etc/resolv.conf, if set.
-s
This option tells namednot to send the query to the next nameserver if any server responds
with a SERVFAIL response, which is the reverse of normal stub
resolver behavior.
-ttype
This option specifies the query type. The type argument can be any recognized query type:
CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc.
When no query type is specified, host automatically selects an
appropriate query type. By default, it looks for A, AAAA, and MX
records. If the -C option is given, queries are made for SOA
records. If name is a dotted-decimal IPv4 address or
colon-delimited IPv6 address, host queries for PTR records.
If a query type of IXFR is chosen, the starting serial number can be
specified by appending an equals sign (=), followed by the starting serial
number, e.g., -tIXFR=12345678.
-T; -U
This option specifies TCP or UDP. By default, host uses UDP when making queries; the
-T option makes it use a TCP connection when querying the name
server. TCP is automatically selected for queries that require
it, such as zone transfer (AXFR) requests. Type ANY queries default
to TCP, but can be forced to use UDP initially via -U.
-mflag
This option sets memory usage debugging: the flag can be record, usage, or
trace. The -m option can be specified more than once to set
multiple flags.
-v
This option sets verbose output, and is equivalent to the -d debug option. Verbose output
can also be enabled by setting the debug option in
/etc/resolv.conf.
-V
This option prints the version number and exits.
-w
This option sets “wait forever”: the query timeout is set to the maximum possible. See
also the -W option.
-Wwait
This options sets the length of the wait timeout, indicating that named should wait for up to wait seconds for a reply. If wait is
less than 1, the wait interval is set to 1 second.
By default, host waits for 5 seconds for UDP responses and 10
seconds for TCP connections. These defaults can be overridden by the
timeout option in /etc/resolv.conf.
If host has been built with IDN (internationalized domain name)
support, it can accept and display non-ASCII domain names. host
appropriately converts character encoding of a domain name before sending
a request to a DNS server or displaying a reply from the server.
To turn off IDN support, define the IDN_DISABLE
environment variable. IDN support is disabled if the variable is set
when host runs.
mdig is a multiple/pipelined query version of dig: instead of
waiting for a response after sending each query, it begins by sending
all queries. Responses are displayed in the order in which they are
received, not in the order the corresponding queries were sent.
mdig options are a subset of the dig options, and are divided
into “anywhere options,” which can occur anywhere, “global options,” which
must occur before the query name (or they are ignored with a warning),
and “local options,” which apply to the next query on the command line.
The @server option is a mandatory global option. It is the name or IP
address of the name server to query. (Unlike dig, this value is not
retrieved from /etc/resolv.conf.) It can be an IPv4 address in
dotted-decimal notation, an IPv6 address in colon-delimited notation, or
a hostname. When the supplied server argument is a hostname,
mdig resolves that name before querying the name server.
mdig provides a number of query options which affect the way in
which lookups are made and the results displayed. Some of these set or
reset flag bits in the query header, some determine which sections of
the answer get printed, and others determine the timeout and retry
strategies.
Each query option is identified by a keyword preceded by a plus sign
(+). Some keywords set or reset an option. These may be preceded by
the string no to negate the meaning of that keyword. Other keywords
assign values to options like the timeout interval. They have the form
+keyword=value.
This option makes mdig operate in batch mode by reading a list
of lookup requests to process from the file filename. The file
contains a number of queries, one per line. Each entry in the file
should be organized in the same way they would be presented as queries
to mdig using the command-line interface.
-h
This option causes mdig to print detailed help information, with the full list
of options, and exit.
-v
This option causes mdig to print the version number and exit.
This option forces mdig to only use IPv4 query transport.
-6
This option forces mdig to only use IPv6 query transport.
-baddress
This option sets the source IP address of the query to
address. This must be a valid address on one of the host’s network
interfaces or “0.0.0.0” or “::”. An optional port may be specified by
appending “#<port>”
-m
This option enables memory usage debugging.
-pport#
This option is used when a non-standard port number is to be
queried. port# is the port number that mdig sends its
queries to, instead of the standard DNS port number 53. This option is
used to test a name server that has been configured to listen for
queries on a non-standard port number.
The global query options are:
+[no]additional
This option displays [or does not display] the additional section of a reply. The
default is to display it.
+[no]all
This option sets or clears all display flags.
+[no]answer
This option displays [or does not display] the answer section of a reply. The default
is to display it.
+[no]authority
This option displays [or does not display] the authority section of a reply. The
default is to display it.
+[no]besteffort
This option attempts to display [or does not display] the contents of messages which are malformed. The
default is to not display malformed answers.
+burst
This option delays queries until the start of the next second.
+[no]cl
This option displays [or does not display] the CLASS when printing the record.
+[no]comments
This option toggles the display of comment lines in the output. The default is to
print comments.
+[no]continue
This option toggles continuation on errors (e.g. timeouts).
+[no]crypto
This option toggles the display of cryptographic fields in DNSSEC records. The
contents of these fields are unnecessary to debug most DNSSEC
validation failures and removing them makes it easier to see the
common failures. The default is to display the fields. When omitted,
they are replaced by the string “[omitted]”; in the DNSKEY case, the
key ID is displayed as the replacement, e.g., [keyid=value].
+dscp[=value]
This option sets the DSCP code point to be used when sending the query. Valid DSCP
code points are in the range [0…63]. By default no code point is
explicitly set.
+[no]multiline
This option toggles printing of records, like the SOA records, in a verbose multi-line format
with human-readable comments. The default is to print each record on
a single line, to facilitate machine parsing of the mdig output.
+[no]question
This option prints [or does not print] the question section of a query when an answer
is returned. The default is to print the question section as a
comment.
+[no]rrcomments
This option toggles the display of per-record comments in the output (for example,
human-readable key information about DNSKEY records). The default is
not to print record comments unless multiline mode is active.
+[no]short
This option provides [or does not provide] a terse answer. The default is to print the answer in a
verbose form.
+split=W
This option splits long hex- or base64-formatted fields in resource records into
chunks of W characters (where W is rounded up to the nearest
multiple of 4). +nosplit or +split=0 causes fields not to be
split. The default is 56 characters, or 44 characters when
multiline mode is active.
+[no]tcp
This option uses [or does not use] TCP when querying name servers. The default behavior
is to use UDP.
+[no]ttlid
This option displays [or does not display] the TTL when printing the record.
+[no]ttlunits
This option displays [or does not display] the TTL in friendly human-readable time
units of “s”, “m”, “h”, “d”, and “w”, representing seconds, minutes,
hours, days, and weeks. This implies +ttlid.
+[no]vc
This option uses [or does not use] TCP when querying name servers. This alternate
syntax to +[no]tcp is provided for backwards compatibility. The
vc stands for “virtual circuit”.
This option sets the query class to class. It can be any valid
query class which is supported in BIND 9. The default query class is
“IN”.
-ttype
This option sets the query type to type. It can be any valid
query type which is supported in BIND 9. The default query type is “A”,
unless the -x option is supplied to indicate a reverse lookup with
the “PTR” query type.
-xaddr
Reverse lookups - mapping addresses to names - are simplified by
this option. addr is an IPv4 address in dotted-decimal
notation, or a colon-delimited IPv6 address. mdig automatically
performs a lookup for a query name like 11.12.13.10.in-addr.arpa and
sets the query type and class to PTR and IN respectively. By default,
IPv6 addresses are looked up using nibble format under the IP6.ARPA
domain.
The local query options are:
+[no]aaflag
This is a synonym for +[no]aaonly.
+[no]aaonly
This sets the aa flag in the query.
+[no]adflag
This sets [or does not set] the AD (authentic data) bit in the query. This
requests the server to return whether all of the answer and authority
sections have all been validated as secure, according to the security
policy of the server. AD=1 indicates that all records have been
validated as secure and the answer is not from a OPT-OUT range. AD=0
indicates that some part of the answer was insecure or not validated.
This bit is set by default.
+bufsize=B
This sets the UDP message buffer size advertised using EDNS0 to B
bytes. The maximum and minimum sizes of this buffer are 65535 and 0
respectively. Values outside this range are rounded up or down
appropriately. Values other than zero cause a EDNS query to be
sent.
+[no]cdflag
This sets [or does not set] the CD (checking disabled) bit in the query. This
requests the server to not perform DNSSEC validation of responses.
+[no]cookie=####
This sends [or does not send] a COOKIE EDNS option, with an optional value. Replaying a COOKIE
from a previous response allows the server to identify a previous
client. The default is +nocookie.
+[no]dnssec
This requests that DNSSEC records be sent by setting the DNSSEC OK (DO) bit in
the OPT record in the additional section of the query.
+[no]edns[=#]
This specifies [or does not specify] the EDNS version to query with. Valid values are 0 to 255.
Setting the EDNS version causes an EDNS query to be sent.
+noedns clears the remembered EDNS version. EDNS is set to 0 by
default.
+[no]ednsflags[=#]
This sets the must-be-zero EDNS flag bits (Z bits) to the specified value.
Decimal, hex, and octal encodings are accepted. Setting a named flag
(e.g. DO) is silently ignored. By default, no Z bits are set.
+[no]ednsopt[=code[:value]]
This specifies [or does not specify] an EDNS option with code point code and an optional payload
of value as a hexadecimal string. +noednsopt clears the EDNS
options to be sent.
+[no]expire
This toggles sending of an EDNS Expire option.
+[no]nsid
This toggles inclusion of an EDNS name server ID request when sending a query.
+[no]recurse
This toggles the setting of the RD (recursion desired) bit in the query.
This bit is set by default, which means mdig normally sends
recursive queries.
+retry=T
This sets the number of times to retry UDP queries to server to T
instead of the default, 2. Unlike +tries, this does not include
the initial query.
+[no]subnet=addr[/prefix-length]
This sends [or does not send] an EDNS Client Subnet option with the specified IP
address or network prefix.
mdig+subnet=0.0.0.0/0, or simply mdig+subnet=0
This sends an EDNS client-subnet option with an empty address and a source
prefix-length of zero, which signals a resolver that the client’s
address information must not be used when resolving this query.
+timeout=T
This sets the timeout for a query to T seconds. The default timeout is
5 seconds for UDP transport and 10 for TCP. An attempt to set T
to less than 1 results in a query timeout of 1 second being
applied.
+tries=T
This sets the number of times to try UDP queries to server to T
instead of the default, 3. If T is less than or equal to zero,
the number of tries is silently rounded up to 1.
+udptimeout=T
This sets the timeout between UDP query retries to T.
+[no]unknownformat
This prints [or does not print] all RDATA in unknown RR-type presentation format (see RFC 3597).
The default is to print RDATA for known types in the type’s
presentation format.
+[no]yaml
This toggles printing of the responses in a detailed YAML format.
+[no]zflag
This sets [or does not set] the last unassigned DNS header flag in a DNS query.
This flag is off by default.
named-checkconf checks the syntax, but not the semantics, of a
named configuration file. The file, along with all files included by it, is parsed and checked for syntax
errors. If no file is specified,
/etc/named.conf is read by default.
Note: files that named reads in separate parser contexts, such as
rndc.key and bind.keys, are not automatically read by
named-checkconf. Configuration errors in these files may cause
named to fail to run, even if named-checkconf was successful.
However, named-checkconf can be run on these files explicitly.
When loading a zonefile, this option instructs named to read the journal if it exists.
-l
This option lists all the configured zones. Each line of output contains the zone
name, class (e.g. IN), view, and type (e.g. primary or secondary).
-c
This option specifies that only the “core” configuration should be checked. This suppresses the loading of
plugin modules, and causes all parameters to plugin statements to
be ignored.
-i
This option ignores warnings on deprecated options.
-p
This option prints out the named.conf and included files in canonical form if
no errors were detected. See also the -x option.
-tdirectory
This option instructs named to chroot to directory, so that include directives in the
configuration file are processed as if run by a similarly chrooted
named.
-v
This option prints the version of the named-checkconf program and exits.
-x
When printing the configuration files in canonical form, this option obscures
shared secrets by replacing them with strings of question marks
(?). This allows the contents of named.conf and related files
to be shared - for example, when submitting bug reports -
without compromising private data. This option cannot be used without
-p.
-z
This option performs a test load of all zones of type primary found in named.conf.
filename
This indicates the name of the configuration file to be checked. If not specified,
it defaults to /etc/named.conf.
named-checkzone checks the syntax and integrity of a zone file. It
performs the same checks as named does when loading a zone. This
makes named-checkzone useful for checking zone files before
configuring them into a name server.
This option sets quiet mode, which only sets an exit code to indicate
successful or failed completion.
-v
This option prints the version of the named-checkzone program and exits.
-j
When loading a zone file, this option tells named to read the journal if it exists. The journal
file name is assumed to be the zone file name with the
string .jnl appended.
-Jfilename
When loading the zone file, this option tells named to read the journal from the given file, if
it exists. This implies -j.
-cclass
This option specifies the class of the zone. If not specified, IN is assumed.
-imode
This option performs post-load zone integrity checks. Possible modes are
full (the default), full-sibling, local,
local-sibling, and none.
Mode full checks that MX records refer to A or AAAA records
(both in-zone and out-of-zone hostnames). Mode local only
checks MX records which refer to in-zone hostnames.
Mode full checks that SRV records refer to A or AAAA records
(both in-zone and out-of-zone hostnames). Mode local only
checks SRV records which refer to in-zone hostnames.
Mode full checks that delegation NS records refer to A or AAAA
records (both in-zone and out-of-zone hostnames). It also checks that
glue address records in the zone match those advertised by the child.
Mode local only checks NS records which refer to in-zone
hostnames or verifies that some required glue exists, i.e., when the
name server is in a child zone.
Modes full-sibling and local-sibling disable sibling glue
checks, but are otherwise the same as full and local,
respectively.
Mode none disables the checks.
-fformat
This option specifies the format of the zone file. Possible formats are
text (the default), raw, and map.
-Fformat
This option specifies the format of the output file specified. For
named-checkzone, this does not have any effect unless it dumps
the zone contents.
Possible formats are text (the default), which is the standard
textual representation of the zone, and map, raw, and raw=N, which
store the zone in a binary format for rapid loading by named.
raw=N specifies the format version of the raw zone file: if N is
0, the raw file can be read by any version of named; if N is 1, the
file can only be read by release 9.9.0 or higher. The default is 1.
-kmode
This option performs check-names checks with the specified failure mode.
Possible modes are fail, warn (the default), and ignore.
-lttl
This option sets a maximum permissible TTL for the input file. Any record with a
TTL higher than this value causes the zone to be rejected. This
is similar to using the max-zone-ttl option in named.conf.
-Lserial
When compiling a zone to raw or map format, this option sets the “source
serial” value in the header to the specified serial number. This is
expected to be used primarily for testing purposes.
-mmode
This option specifies whether MX records should be checked to see if they are
addresses. Possible modes are fail, warn (the default), and
ignore.
-Mmode
This option checks whether a MX record refers to a CNAME. Possible modes are
fail, warn (the default), and ignore.
-nmode
This option specifies whether NS records should be checked to see if they are
addresses. Possible modes are fail, warn (the default), and ignore.
-ofilename
This option writes the zone output to filename. If filename is -, then
the zone output is written to standard output.
-rmode
This option checks for records that are treated as different by DNSSEC but are
semantically equal in plain DNS. Possible modes are fail,
warn (the default), and ignore.
-sstyle
This option specifies the style of the dumped zone file. Possible styles are
full (the default) and relative. The full format is most
suitable for processing automatically by a separate script.
The relative format is more human-readable and is thus
suitable for editing by hand. This does not have any effect unless it dumps
the zone contents. It also does not have any meaning if the output format
is not text.
-Smode
This option checks whether an SRV record refers to a CNAME. Possible modes are
fail, warn (the default), and ignore.
-tdirectory
This option tells named to chroot to directory, so that include directives in the
configuration file are processed as if run by a similarly chrooted
named.
-Tmode
This option checks whether Sender Policy Framework (SPF) records exist and issues a
warning if an SPF-formatted TXT record is not also present. Possible
modes are warn (the default) and ignore.
-wdirectory
This option instructs named to chdir to directory, so that relative filenames in master file
$INCLUDE directives work. This is similar to the directory clause in
named.conf.
-D
This option dumps the zone file in canonical format.
-Wmode
This option specifies whether to check for non-terminal wildcards. Non-terminal
wildcards are almost always the result of a failure to understand the
wildcard matching algorithm (RFC 4592). Possible modes are warn
(the default) and ignore.
zonename
This indicates the domain name of the zone being checked.
named-compilezone checks the syntax and integrity of a zone file,
and dumps the zone contents to a specified file in a specified format.
It applies strict check levels by default, since the
dump output is used as an actual zone file loaded by named.
When manually specified otherwise, the check levels must at least be as
strict as those specified in the named configuration file.
This option sets quiet mode, which only sets an exit code to indicate
successful or failed completion.
-v
This option prints the version of the named-checkzone program and exits.
-j
When loading a zone file, this option tells named to read the journal if it exists. The journal
file name is assumed to be the zone file name with the
string .jnl appended.
-Jfilename
When loading the zone file, this option tells named to read the journal from the given file, if
it exists. This implies -j.
-cclass
This option specifies the class of the zone. If not specified, IN is assumed.
-imode
This option performs post-load zone integrity checks. Possible modes are
full (the default), full-sibling, local,
local-sibling, and none.
Mode full checks that MX records refer to A or AAAA records
(both in-zone and out-of-zone hostnames). Mode local only
checks MX records which refer to in-zone hostnames.
Mode full checks that SRV records refer to A or AAAA records
(both in-zone and out-of-zone hostnames). Mode local only
checks SRV records which refer to in-zone hostnames.
Mode full checks that delegation NS records refer to A or AAAA
records (both in-zone and out-of-zone hostnames). It also checks that
glue address records in the zone match those advertised by the child.
Mode local only checks NS records which refer to in-zone
hostnames or verifies that some required glue exists, i.e., when the
name server is in a child zone.
Modes full-sibling and local-sibling disable sibling glue
checks, but are otherwise the same as full and local,
respectively.
Mode none disables the checks.
-fformat
This option specifies the format of the zone file. Possible formats are
text (the default), raw, and map.
-Fformat
This option specifies the format of the output file specified. For
named-checkzone, this does not have any effect unless it dumps
the zone contents.
Possible formats are text (the default), which is the standard
textual representation of the zone, and map, raw, and raw=N, which
store the zone in a binary format for rapid loading by named.
raw=N specifies the format version of the raw zone file: if N is
0, the raw file can be read by any version of named; if N is 1, the
file can only be read by release 9.9.0 or higher. The default is 1.
-kmode
This option performs check-names checks with the specified failure mode.
Possible modes are fail (the default), warn, and ignore.
-lttl
This option sets a maximum permissible TTL for the input file. Any record with a
TTL higher than this value causes the zone to be rejected. This
is similar to using the max-zone-ttl option in named.conf.
-Lserial
When compiling a zone to raw or map format, this option sets the “source
serial” value in the header to the specified serial number. This is
expected to be used primarily for testing purposes.
-mmode
This option specifies whether MX records should be checked to see if they are
addresses. Possible modes are fail, warn (the default), and
ignore.
-Mmode
This option checks whether a MX record refers to a CNAME. Possible modes are
fail, warn (the default), and ignore.
-nmode
This option specifies whether NS records should be checked to see if they are
addresses. Possible modes are fail (the default), warn, and
ignore.
-ofilename
This option writes the zone output to filename. If filename is -, then
the zone output is written to standard output. This is mandatory for named-compilezone.
-rmode
This option checks for records that are treated as different by DNSSEC but are
semantically equal in plain DNS. Possible modes are fail,
warn (the default), and ignore.
-sstyle
This option specifies the style of the dumped zone file. Possible styles are
full (the default) and relative. The full format is most
suitable for processing automatically by a separate script.
The relative format is more human-readable and is thus
suitable for editing by hand.
-Smode
This option checks whether an SRV record refers to a CNAME. Possible modes are
fail, warn (the default), and ignore.
-tdirectory
This option tells named to chroot to directory, so that include directives in the
configuration file are processed as if run by a similarly chrooted
named.
-Tmode
This option checks whether Sender Policy Framework (SPF) records exist and issues a
warning if an SPF-formatted TXT record is not also present. Possible
modes are warn (the default) and ignore.
-wdirectory
This option instructs named to chdir to directory, so that relative filenames in master file
$INCLUDE directives work. This is similar to the directory clause in
named.conf.
-D
This option dumps the zone file in canonical format. This is always enabled for
named-compilezone.
-Wmode
This option specifies whether to check for non-terminal wildcards. Non-terminal
wildcards are almost always the result of a failure to understand the
wildcard matching algorithm (RFC 4592). Possible modes are warn
(the default) and ignore.
zonename
This indicates the domain name of the zone being checked.
named-journalprint scans the contents of a zone journal file,
printing it in a human-readable form, or, optionally, converting it
to a different journal file format.
Journal files are automatically created by named when changes are
made to dynamic zones (e.g., by nsupdate). They record each addition
or deletion of a resource record, in binary format, allowing the changes
to be re-applied to the zone when the server is restarted after a
shutdown or crash. By default, the name of the journal file is formed by
appending the extension .jnl to the name of the corresponding zone
file.
named-journalprint converts the contents of a given journal file
into a human-readable text format. Each line begins with add or del,
to indicate whether the record was added or deleted, and continues with
the resource record in master-file format.
The -c (compact) option provides a mechanism to reduce the size of
a journal by removing (most/all) transactions prior to the specified
serial number. Note: this option must not be used while named is
running, and can cause data loss if the zone file has not been updated
to contain the data being removed from the journal. Use with extreme caution.
The -x option causes additional data about the journal file to be
printed at the beginning of the output and before each group of changes.
The -u (upgrade) and -d (downgrade) options recreate the journal
file with a modified format version. The existing journal file is
replaced. -d writes out the journal in the format used by
versions of BIND up to 9.16.11; -u writes it out in the format used
by versions since 9.16.13. (9.16.12 is omitted due to a journal-formatting
bug in that release.) Note that these options must not be used while
named is running.
named-nzd2nzf converts an NZD database to NZF format and prints it
to standard output. This can be used to review the configuration of
zones that were added to named via rndcaddzone. It can also be
used to restore the old file format when rolling back from a newer
version of BIND to an older version.
named.conf is the configuration file for named. Statements are
enclosed in braces and terminated with a semi-colon. Clauses in the
statements are also semi-colon terminated. The usual comment styles are
supported:
named is a Domain Name System (DNS) server, part of the BIND 9
distribution from ISC. For more information on the DNS, see RFC 1033,
RFC 1034, and RFC 1035.
When invoked without arguments, named reads the default
configuration file /etc/named.conf, reads any initial data, and
listens for queries.
This option tells named to use only IPv4, even if the host machine is capable of IPv6. -4 and
-6 are mutually exclusive.
-6
This option tells named to use only IPv6, even if the host machine is capable of IPv4. -4 and
-6 are mutually exclusive.
-cconfig-file
This option tells named to use config-file as its configuration file instead of the default,
/etc/named.conf. To ensure that the configuration file
can be reloaded after the server has changed its working directory
due to to a possible directory option in the configuration file,
config-file should be an absolute pathname.
-C
This option prints out the default built-in configuration and exits.
NOTE: This is for debugging purposes only and is not an
accurate representation of the actual configuration used by named
at runtime.
-ddebug-level
This option sets the daemon’s debug level to debug-level. Debugging traces from
named become more verbose as the debug level increases.
-Dstring
This option specifies a string that is used to identify a instance of named
in a process listing. The contents of string are not examined.
-Eengine-name
When applicable, this option specifies the hardware to use for cryptographic
operations, such as a secure key store used for signing.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL
engine identifier that drives the cryptographic accelerator or
hardware service module (usually pkcs11). When BIND is
built with native PKCS#11 cryptography (--enable-native-pkcs11), it
defaults to the path of the PKCS#11 provider library specified via
--with-pkcs11.
-f
This option runs the server in the foreground (i.e., do not daemonize).
-g
This option runs the server in the foreground and forces all logging to stderr.
-Llogfile
This option sets the log to the file logfile by default, instead of the system log.
-Moption
This option sets the default (comma-separated) memory context
options. The possible flags are:
external: use system-provided memory allocation functions; this
is the implicit default.
internal: use the internal memory manager.
fill: fill blocks of memory with tag values when they are
allocated or freed, to assist debugging of memory problems; this is
the implicit default if named has been compiled with
--enable-developer.
nofill: disable the behavior enabled by fill; this is the
implicit default unless named has been compiled with
--enable-developer.
-mflag
This option turns on memory usage debugging flags. Possible flags are usage,
trace, record, size, and mctx. These correspond to the
ISC_MEM_DEBUGXXXX flags described in <isc/mem.h>.
-n#cpus
This option controls the number of CPUs that named assumes the
presence of. If not specified, named tries to determine the
number of CPUs present automatically; if it fails, a single CPU is
assumed to be present.
named creates two threads per each CPU present (one thread for
receiving and sending client traffic and another thread for sending
and receiving resolver traffic) and then on top of that a single
thread for handling time-based events.
-pport
This option listens for queries on port. If not specified, the default is
port 53.
-s
This option writes memory usage statistics to stdout on exit.
Note
This option is mainly of interest to BIND 9 developers and may be
removed or changed in a future release.
-S#max-socks
This option allows named to use up to #max-socks sockets. The default value is
21000 on systems built with default configuration options, and 4096
on systems built with configure--with-tuning=small.
Warning
This option should be unnecessary for the vast majority of users.
The use of this option could even be harmful, because the specified
value may exceed the limitation of the underlying system API. It
is therefore set only when the default configuration causes
exhaustion of file descriptors and the operational environment is
known to support the specified number of sockets. Note also that
the actual maximum number is normally slightly fewer than the
specified value, because named reserves some file descriptors
for its internal use.
-tdirectory
This option tells named to chroot to directory after processing the command-line arguments, but
before reading the configuration file.
Warning
This option should be used in conjunction with the -u option,
as chrooting a process running as root doesn’t enhance security on
most systems; the way chroot is defined allows a process
with root privileges to escape a chroot jail.
-U#listeners
This option tells named the number of #listeners worker threads to listen on, for incoming UDP packets on
each address. If not specified, named calculates a default
value based on the number of detected CPUs: 1 for 1 CPU, and the
number of detected CPUs minus one for machines with more than 1 CPU.
This cannot be increased to a value higher than the number of CPUs.
If -n has been set to a higher value than the number of detected
CPUs, then -U may be increased as high as that value, but no
higher. On Windows, the number of UDP listeners is hardwired to 1 and
this option has no effect.
-uuser
This option sets the setuid to user after completing privileged operations, such as
creating sockets that listen on privileged ports.
Note
On Linux, named uses the kernel’s capability mechanism to drop
all root privileges except the ability to bind to a
privileged port and set process resource limits. Unfortunately,
this means that the -u option only works when named is run
on kernel 2.2.18 or later, or kernel 2.3.99-pre3 or later, since
previous kernels did not allow privileges to be retained after
setuid.
-v
This option reports the version number and exits.
-V
This option reports the version number, build options, supported
cryptographics algorithms, and exits.
-Xlock-file
This option acquires a lock on the specified file at runtime; this helps to
prevent duplicate named instances from running simultaneously.
Use of this option overrides the lock-file option in
named.conf. If set to none, the lock file check is disabled.
-xcache-file
This option loads data from cache-file into the cache of the default view.
Warning
This option must not be used in normal operations. It is only of interest to BIND 9
developers and may be removed or changed in a future release.
The named configuration file is too complex to describe in detail
here. A complete description is provided in the BIND 9 Administrator
Reference Manual.
named inherits the umask (file creation mode mask) from the
parent process. If files created by named, such as journal files,
need to have custom permissions, the umask should be set explicitly
in the script used to start the named process.
nsec3hash generates an NSEC3 hash based on a set of NSEC3
parameters. This can be used to check the validity of NSEC3 records in a
signed zone.
If this command is invoked as nsec3hash-r, it takes arguments in
order, matching the first four fields of an NSEC3 record followed by the
domain name: algorithm, flags, iterations, salt, domain. This makes it
convenient to copy and paste a portion of an NSEC3 or NSEC3PARAM record
into a command line to confirm the correctness of an NSEC3 hash.
This is a number indicating the hash algorithm. Currently the only supported
hash algorithm for NSEC3 is SHA-1, which is indicated by the number
1; consequently “1” is the only useful value for this argument.
flags
This is provided for compatibility with NSEC3 record presentation format, but
is ignored since the flags do not affect the hash.
iterations
This is the number of additional times the hash should be performed.
nslookup is a program to query Internet domain name servers.
nslookup has two modes: interactive and non-interactive. Interactive
mode allows the user to query name servers for information about various
hosts and domains or to print a list of hosts in a domain.
Non-interactive mode prints just the name and requested
information for a host or domain.
Interactive mode is entered in the following cases:
when no arguments are given (the default name server is used);
when the first argument is a hyphen (-) and the second argument is
the host name or Internet address of a name server.
Non-interactive mode is used when the name or Internet address of the
host to be looked up is given as the first argument. The optional second
argument specifies the host name or address of a name server.
Options can also be specified on the command line if they precede the
arguments and are prefixed with a hyphen. For example, to change the
default query type to host information, with an initial timeout of 10
seconds, type:
nslookup-query=hinfo-timeout=10
The -version option causes nslookup to print the version number
and immediately exit.
This command looks up information for host using the current default server or
using server, if specified. If host is an Internet address and the
query type is A or PTR, the name of the host is returned. If host is
a name and does not have a trailing period (.), the search list is used
to qualify the name.
To look up a host not in the current domain, append a period to the
name.
serverdomain | lserverdomain
These commands change the default server to domain; lserver uses the initial
server to look up information about domain, while server uses the
current default server. If an authoritative answer cannot be found,
the names of servers that might have the answer are returned.
root
This command is not implemented.
finger
This command is not implemented.
ls
This command is not implemented.
view
This command is not implemented.
help
This command is not implemented.
?
This command is not implemented.
exit
This command exits the program.
setkeyword[=value]
This command is used to change state information that affects the
lookups. Valid keywords are:
all
This keyword prints the current values of the frequently used options to
set. Information about the current default server and host is
also printed.
class=value
This keyword changes the query class to one of:
IN
the Internet class
CH
the Chaos class
HS
the Hesiod class
ANY
wildcard
The class specifies the protocol group of the information. The default
is IN; the abbreviation for this keyword is cl.
nodebug
This keyword turns on or off the display of the full response packet, and any
intermediate response packets, when searching. The default for this keyword is
nodebug; the abbreviation for this keyword is [no]deb.
nod2
This keyword turns debugging mode on or off. This displays more about what
nslookup is doing. The default is nod2.
domain=name
This keyword sets the search list to name.
nosearch
If the lookup request contains at least one period, but does not end
with a trailing period, this keyword appends the domain names in the domain
search list to the request until an answer is received. The default is search.
port=value
This keyword changes the default TCP/UDP name server port to value from
its default, port 53. The abbreviation for this keyword is po.
querytype=value | type=value
This keyword changes the type of the information query to value. The
defaults are A and then AAAA; the abbreviations for these keywords are
q and ty.
Please note that it is only possible to specify one query type. Only the default
behavior looks up both when an alternative is not specified.
norecurse
This keyword tells the name server to query other servers if it does not have
the information. The default is recurse; the abbreviation for this
keyword is [no]rec.
ndots=number
This keyword sets the number of dots (label separators) in a domain that
disables searching. Absolute names always stop searching.
retry=number
This keyword sets the number of retries to number.
timeout=number
This keyword changes the initial timeout interval to wait for a reply to
number, in seconds.
novc
This keyword indicates that a virtual circuit should always be used when sending requests to the server.
novc is the default.
nofail
This keyword tries the next nameserver if a nameserver responds with SERVFAIL or
a referral (nofail), or terminates the query (fail) on such a response. The
default is nofail.
If nslookup has been built with IDN (internationalized domain name)
support, it can accept and display non-ASCII domain names. nslookup
appropriately converts character encoding of a domain name before sending
a request to a DNS server or displaying a reply from the server.
To turn off IDN support, define the IDN_DISABLE
environment variable. IDN support is disabled if the variable is set
when nslookup runs, or when the standard output is not a tty.
nsupdate is used to submit Dynamic DNS Update requests, as defined in
RFC 2136, to a name server. This allows resource records to be added or
removed from a zone without manually editing the zone file. A single
update request can contain requests to add or remove more than one
resource record.
Zones that are under dynamic control via nsupdate or a DHCP server
should not be edited by hand. Manual edits could conflict with dynamic
updates and cause data to be lost.
The resource records that are dynamically added or removed with
nsupdate must be in the same zone. Requests are sent to the
zone’s primary server, which is identified by the MNAME field of the
zone’s SOA record.
Transaction signatures can be used to authenticate the Dynamic DNS
updates. These use the TSIG resource record type described in RFC 2845,
the SIG(0) record described in RFC 2535 and RFC 2931, or GSS-TSIG as
described in RFC 3645.
TSIG relies on a shared secret that should only be known to nsupdate
and the name server. For instance, suitable key and server
statements are added to /etc/named.conf so that the name server
can associate the appropriate secret key and algorithm with the IP
address of the client application that is using TSIG
authentication. ddns-confgen can generate suitable
configuration fragments. nsupdate uses the -y or -k options
to provide the TSIG shared secret; these options are mutually exclusive.
SIG(0) uses public key cryptography. To use a SIG(0) key, the public key
must be stored in a KEY record in a zone served by the name server.
GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched
on with the -g flag. A non-standards-compliant variant of GSS-TSIG
used by Windows 2000 can be switched on with the -o flag.
This option sets debug mode, which provides tracing information about the update
requests that are made and the replies received from the name server.
-D
This option sets extra debug mode.
-i
This option forces interactive mode, even when standard input is not a terminal.
-kkeyfile
This option indicates the file containing the TSIG authentication key. Keyfiles may be in
two formats: a single file containing a named.conf-format key
statement, which may be generated automatically by ddns-confgen;
or a pair of files whose names are of the format
K{name}.+157.+{random}.key and
K{name}.+157.+{random}.private, which can be generated by
dnssec-keygen. The -k option can also be used to specify a SIG(0)
key used to authenticate Dynamic DNS update requests. In this case,
the key specified is not an HMAC-MD5 key.
-l
This option sets local-host only mode, which sets the server address to localhost
(disabling the server so that the server address cannot be
overridden). Connections to the local server use a TSIG key
found in /var/run/named/session.key, which is automatically
generated by named if any local primary zone has set
update-policy to local. The location of this key file can be
overridden with the -k option.
-Llevel
This option sets the logging debug level. If zero, logging is disabled.
-pport
This option sets the port to use for connections to a name server. The default is
53.
-P
This option prints the list of private BIND-specific resource record types whose
format is understood by nsupdate. See also the -T option.
-rudpretries
This option sets the number of UDP retries. The default is 3. If zero, only one update
request is made.
-ttimeout
This option sets the maximum time an update request can take before it is aborted. The
default is 300 seconds. If zero, the timeout is disabled.
-T
This option prints the list of IANA standard resource record types whose format is
understood by nsupdate. nsupdate exits after the lists
are printed. The -T option can be combined with the -P
option.
Other types can be entered using TYPEXXXXX where XXXXX is the
decimal value of the type with no leading zeros. The rdata, if
present, is parsed using the UNKNOWN rdata format, (<backslash>
<hash> <space> <length> <space> <hexstring>).
-uudptimeout
This option sets the UDP retry interval. The default is 3 seconds. If zero, the
interval is computed from the timeout interval and number of UDP
retries.
-v
This option specifies that TCP should be used even for small update requests. By default, nsupdate uses
UDP to send update requests to the name server unless they are too
large to fit in a UDP request, in which case TCP is used. TCP may
be preferable when a batch of update requests is made.
-V
This option prints the version number and exits.
-y[hmac:]keyname:secret
This option sets the literal TSIG authentication key. keyname is the name of the key,
and secret is the base64 encoded shared secret. hmac is the
name of the key algorithm; valid choices are hmac-md5,
hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, or
hmac-sha512. If hmac is not specified, the default is
hmac-md5, or if MD5 was disabled, hmac-sha256.
NOTE: Use of the -y option is discouraged because the shared
secret is supplied as a command-line argument in clear text. This may
be visible in the output from ps1 or in a history file maintained by
the user’s shell.
nsupdate reads input from filename or standard input. Each
command is supplied on exactly one line of input. Some commands are for
administrative purposes; others are either update instructions or
prerequisite checks on the contents of the zone. These checks set
conditions that some name or set of resource records (RRset) either
exists or is absent from the zone. These conditions must be met if the
entire update request is to succeed. Updates are rejected if the
tests for the prerequisite conditions fail.
Every update request consists of zero or more prerequisites and zero or
more updates. This allows a suitably authenticated update request to
proceed if some specified resource records are either present or missing from
the zone. A blank input line (or the send command) causes the
accumulated commands to be sent as one Dynamic DNS update request to the
name server.
The command formats and their meanings are as follows:
serverservernameport
This command sends all dynamic update requests to the name server servername.
When no server statement is provided, nsupdate sends updates
to the primary server of the correct zone. The MNAME field of that
zone’s SOA record identify the primary server for that zone.
port is the port number on servername where the dynamic
update requests are sent. If no port number is specified, the default
DNS port number of 53 is used.
Note
This command has no effect when GSS-TSIG is in use.
localaddressport
This command sends all dynamic update requests using the local address. When
no local statement is provided, nsupdate sends updates using
an address and port chosen by the system. port can also
be used to force requests to come from a specific port. If no port number
is specified, the system assigns one.
zonezonename
This command specifies that all updates are to be made to the zone zonename.
If no zone statement is provided, nsupdate attempts to
determine the correct zone to update based on the rest of the input.
classclassname
This command specifies the default class. If no class is specified, the default
class is IN.
ttlseconds
This command specifies the default time-to-live, in seconds, for records to be added. The value
none clears the default TTL.
keyhmac:keynamesecret
This command specifies that all updates are to be TSIG-signed using the
keyname-secret pair. If hmac is specified, it sets
the signing algorithm in use. The default is hmac-md5; if MD5
was disabled, the default is hmac-sha256. The key command overrides any key
specified on the command line via -y or -k.
gsstsig
This command uses GSS-TSIG to sign the updates. This is equivalent to specifying
-g on the command line.
oldgsstsig
This command uses the Windows 2000 version of GSS-TSIG to sign the updates. This is
equivalent to specifying -o on the command line.
realm[realm_name]
When using GSS-TSIG, this command specifies the use of realm_name rather than the default realm
in krb5.conf. If no realm is specified, the saved realm is
cleared.
check-names[yes_or_no]
This command turns on or off check-names processing on records to be added.
Check-names has no effect on prerequisites or records to be deleted.
By default check-names processing is on. If check-names processing
fails, the record is not added to the UPDATE message.
prereqnxdomaindomain-name
This command requires that no resource record of any type exist with the name
domain-name.
prereqyxdomaindomain-name
This command requires that domain-name exist (as at least one resource
record, of any type).
prereqnxrrsetdomain-nameclasstype
This command requires that no resource record exist of the specified type,
class, and domain-name. If class is omitted, IN (Internet)
is assumed.
prereqyxrrsetdomain-nameclasstype
This command requires that a resource record of the specified type,
class and domain-name exist. If class is omitted, IN
(internet) is assumed.
prereqyxrrsetdomain-nameclasstypedata
With this command, the data from each set of prerequisites of this form sharing a
common type, class, and domain-name are combined to form
a set of RRs. This set of RRs must exactly match the set of RRs
existing in the zone at the given type, class, and
domain-name. The data are written in the standard text
representation of the resource record’s RDATA.
updatedeletedomain-namettlclasstypedata
This command deletes any resource records named domain-name. If type and
data are provided, only matching resource records are removed.
The Internet class is assumed if class is not supplied. The
ttl is ignored, and is only allowed for compatibility.
updateadddomain-namettlclasstypedata
This command adds a new resource record with the specified ttl, class, and
data.
show
This command displays the current message, containing all of the prerequisites and
updates specified since the last send.
send
This command sends the current message. This is equivalent to entering a blank
line.
answer
This command displays the answer.
debug
This command turns on debugging.
version
This command prints the version number.
help
This command prints a list of commands.
Lines beginning with a semicolon (;) are comments and are ignored.
The examples below show how nsupdate can be used to insert and
delete resource records from the example.com zone. Notice that the
input in each example contains a trailing blank line, so that a group of
commands is sent as one dynamic update request to the primary name
server for example.com.
Any A records for oldhost.example.com are deleted, and an A record
for newhost.example.com with IP address 172.16.1.1 is added. The
newly added record has a TTL of 1 day (86400 seconds).
The prerequisite condition tells the name server to verify that there are
no resource records of any type for nickname.example.com. If there
are, the update request fails. If this name does not exist, a CNAME for
it is added. This ensures that when the CNAME is added, it cannot
conflict with the long-standing rule in RFC 1034 that a name must not
exist as any other record type if it exists as a CNAME. (The rule has
been updated for DNSSEC in RFC 2535 to allow CNAMEs to have RRSIG,
DNSKEY, and NSEC records.)
The TSIG key is redundantly stored in two separate files. This is a
consequence of nsupdate using the DST library for its cryptographic
operations, and may change in future releases.
pkcs11-destroy destroys keys stored in a PKCS#11 device, identified
by their ID or label.
Matching keys are displayed before being destroyed. By default, there is
a five-second delay to allow the user to interrupt the process before
the destruction takes place.
This option specifies the PKCS#11 provider module. This must be the full path to a
shared library object implementing the PKCS#11 API for the device.
-sslot
This option opens the session with the given PKCS#11 slot. The default is slot 0.
-iID
This option destroys keys with the given object ID.
-llabel
This option destroys keys with the given label.
-pPIN
This option specifies the PIN for the device. If no PIN is provided on the command
line, pkcs11-destroy prompts for it.
-wseconds
This option specifies how long, in seconds, to pause before carrying out key destruction. The
default is 5 seconds. If set to 0, destruction is
immediate.
This option specifies the key algorithm class: supported classes are RSA, DSA, DH,
ECC, and ECX. In addition to these strings, the algorithm can be
specified as a DNSSEC signing algorithm to be used with this
key; for example, NSEC3RSASHA1 maps to RSA, ECDSAP256SHA256 maps to
ECC, and ED25519 to ECX. The default class is RSA.
-bkeysize
This option creates the key pair with keysize bits of prime. For ECC keys, the
only valid values are 256 and 384, and the default is 256. For ECX
keys, the only valid values are 256 and 456, and the default is 256.
-e
For RSA keys only, this option specifies use of a large exponent.
-iid
This option creates key objects with id. The ID is either an unsigned short 2-byte
or an unsigned long 4-byte number.
-mmodule
This option specifies the PKCS#11 provider module. This must be the full path to a
shared library object implementing the PKCS#11 API for the device.
-P
This option sets the new private key to be non-sensitive and extractable, and
allows the private key data to be read from the PKCS#11 device. The
default is for private keys to be sensitive and non-extractable.
-pPIN
This option specifies the PIN for the device. If no PIN is provided on the command
line, pkcs11-keygen prompts for it.
-q
This option sets quiet mode, which suppresses unnecessary output.
-S
For Diffie-Hellman (DH) keys only, this option specifies use of a special prime of 768-, 1024-,
or 1536-bit size and base (AKA generator) 2. If not specified, bit
size defaults to 1024.
-sslot
This option opens the session with the given PKCS#11 slot. The default is slot 0.
pkcs11-list lists the PKCS#11 objects with ID or label or, by
default, all objects. The object class, label, and ID are displayed for
all keys. For private or secret keys, the extractability attribute is
also displayed, as either true, false, or never.
rndc-confgen generates configuration files for rndc. It can be
used as a convenient alternative to writing the rndc.conf file and
the corresponding controls and key statements in named.conf
by hand. Alternatively, it can be run with the -a option to set up a
rndc.key file and avoid the need for a rndc.conf file and a
controls statement altogether.
This option sets automatic rndc configuration, which creates a file rndc.key
in /etc (or a different sysconfdir specified when BIND
was built) that is read by both rndc and named on startup.
The rndc.key file defines a default command channel and
authentication key allowing rndc to communicate with named on
the local host with no further configuration.
If a more elaborate configuration than that generated by
rndc-confgen-a is required, for example if rndc is to be used
remotely, run rndc-confgen without the -a option
and set up rndc.conf and named.conf as directed.
-Aalgorithm
This option specifies the algorithm to use for the TSIG key. Available choices
are: hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, and
hmac-sha512. The default is hmac-sha256.
-bkeysize
This option specifies the size of the authentication key in bits. The size must be between
1 and 512 bits; the default is the hash size.
-ckeyfile
This option is used with the -a option to specify an alternate location for
rndc.key.
-h
This option prints a short summary of the options and arguments to
rndc-confgen.
-kkeyname
This option specifies the key name of the rndc authentication key. This must be a
valid domain name. The default is rndc-key.
-pport
This option specifies the command channel port where named listens for
connections from rndc. The default is 953.
-saddress
This option specifies the IP address where named listens for command-channel
connections from rndc. The default is the loopback address
127.0.0.1.
-tchrootdir
This option is used with the -a option to specify a directory where named
runs chrooted. An additional copy of the rndc.key is
written relative to this directory, so that it is found by the
chrooted named.
-uuser
This option is used with the -a option to set the owner of the generated rndc.key file.
If -t is also specified, only the file in the chroot
area has its owner changed.
rndc.conf is the configuration file for rndc, the BIND 9 name
server control utility. This file has a similar structure and syntax to
named.conf. Statements are enclosed in braces and terminated with a
semi-colon. Clauses in the statements are also semi-colon terminated.
The usual comment styles are supported:
C style: /* */
C++ style: // to end of line
Unix style: # to end of line
rndc.conf is much simpler than named.conf. The file uses three
statements: an options statement, a server statement, and a key
statement.
The options statement contains five clauses. The default-server
clause is followed by the name or address of a name server. This host
is used when no name server is given as an argument to rndc.
The default-key clause is followed by the name of a key, which is
identified by a key statement. If no keyid is provided on the
rndc command line, and no key clause is found in a matching
server statement, this default key is used to authenticate the
server’s commands and responses. The default-port clause is followed
by the port to connect to on the remote name server. If no port
option is provided on the rndc command line, and no port clause is
found in a matching server statement, this default port is used
to connect. The default-source-address and
default-source-address-v6 clauses can be used to set the IPv4
and IPv6 source addresses respectively.
After the server keyword, the server statement includes a string
which is the hostname or address for a name server. The statement has
three possible clauses: key, port, and addresses. The key
name must match the name of a key statement in the file. The port number
specifies the port to connect to. If an addresses clause is supplied,
these addresses are used instead of the server name. Each address
can take an optional port. If an source-address or
source-address-v6 is supplied, it is used to specify the
IPv4 and IPv6 source address, respectively.
The key statement begins with an identifying string, the name of the
key. The statement has two clauses. algorithm identifies the
authentication algorithm for rndc to use; currently only HMAC-MD5
(for compatibility), HMAC-SHA1, HMAC-SHA224, HMAC-SHA256 (default),
HMAC-SHA384, and HMAC-SHA512 are supported. This is followed by a secret
clause which contains the base-64 encoding of the algorithm’s
authentication key. The base-64 string is enclosed in double quotes.
There are two common ways to generate the base-64 string for the secret.
The BIND 9 program rndc-confgen can be used to generate a random
key, or the mmencode program, also known as mimencode, can be
used to generate a base-64 string from known input. mmencode does
not ship with BIND 9 but is available on many systems. See the Example
section for sample command lines for each.
In the above example, rndc by default uses the server at
localhost (127.0.0.1) and the key called “samplekey”. Commands to the
localhost server use the “samplekey” key, which must also be defined
in the server’s configuration file with the same name and secret. The
key statement indicates that “samplekey” uses the HMAC-SHA256 algorithm
and its secret clause contains the base-64 encoding of the HMAC-SHA256
secret enclosed in double quotes.
If rndc-stestserver is used, then rndc connects to the server
on localhost port 5353 using the key “testkey”.
To generate a random secret with rndc-confgen:
rndc-confgen
A complete rndc.conf file, including the randomly generated key,
is written to the standard output. Commented-out key and
controls statements for named.conf are also printed.
The name server must be configured to accept rndc connections and to
recognize the key specified in the rndc.conf file, using the
controls statement in named.conf. See the sections on the
controls statement in the BIND 9 Administrator Reference Manual for
details.
rndc controls the operation of a name server; it supersedes the
ndc utility. If rndc is
invoked with no command line options or arguments, it prints a short
summary of the supported commands and the available options and their
arguments.
rndc communicates with the name server over a TCP connection,
sending commands authenticated with digital signatures. In the current
versions of rndc and named, the only supported authentication
algorithms are HMAC-MD5 (for compatibility), HMAC-SHA1, HMAC-SHA224,
HMAC-SHA256 (default), HMAC-SHA384, and HMAC-SHA512. They use a shared
secret on each end of the connection, which provides TSIG-style
authentication for the command request and the name server’s response.
All commands sent over the channel must be signed by a key_id known to
the server.
rndc reads a configuration file to determine how to contact the name
server and decide what algorithm and key it should use.
This option indicates source-address as the source address for the connection to the
server. Multiple instances are permitted, to allow setting of both the
IPv4 and IPv6 source addresses.
-cconfig-file
This option indicates config-file as the configuration file instead of the default,
/etc/rndc.conf.
-kkey-file
This option indicates key-file as the key file instead of the default,
/etc/rndc.key. The key in /etc/rndc.key is used to
authenticate commands sent to the server if the config-file does not
exist.
-sserver
server is the name or address of the server which matches a server
statement in the configuration file for rndc. If no server is
supplied on the command line, the host named by the default-server
clause in the options statement of the rndc configuration file
is used.
-pport
This option instructs BIND 9 to send commands to TCP port port instead of its default control
channel port, 953.
-q
This option sets quiet mode, where message text returned by the server is not printed
unless there is an error.
-r
This option instructs rndc to print the result code returned by named
after executing the requested command (e.g., ISC_R_SUCCESS,
ISC_R_FAILURE, etc.).
-V
This option enables verbose logging.
-ykey_id
This option indicates use of the key key_id from the configuration file. For control message validation to succeed, key_id must be known
by named with the same algorithm and secret string. If no key_id is specified,
rndc first looks for a key clause in the server statement of
the server being used, or if no server statement is present for that
host, then in the default-key clause of the options statement. Note that
the configuration file contains shared secrets which are used to send
authenticated control commands to name servers, and should therefore
not have general read or write access.
A list of commands supported by rndc can be seen by running rndc
without arguments.
Currently supported commands are:
addzonezone [class [view]] configuration
This command adds a zone while the server is running. This command requires the
allow-new-zones option to be set to yes. The configuration
string specified on the command line is the zone configuration text
that would ordinarily be placed in named.conf.
The configuration is saved in a file called viewname.nzf (or, if
named is compiled with liblmdb, an LMDB database file called
viewname.nzd). viewname is the name of the view, unless the view
name contains characters that are incompatible with use as a file
name, in which case a cryptographic hash of the view name is used
instead. When named is restarted, the file is loaded into
the view configuration so that zones that were added can persist
after a restart.
This sample addzone command adds the zone example.com to
the default view:
(Note the brackets around and semi-colon after the zone configuration
text.)
See also rndcdelzone and rndcmodzone.
delzone [-clean] zone [class [view]]
This command deletes a zone while the server is running.
If the -clean argument is specified, the zone’s master file (and
journal file, if any) are deleted along with the zone. Without
the -clean option, zone files must be deleted manually. (If the
zone is of type secondary or stub, the files needing to be removed
are reported in the output of the rndcdelzone command.)
If the zone was originally added via rndcaddzone, then it is
removed permanently. However, if it was originally configured in
named.conf, then that original configuration remains in place;
when the server is restarted or reconfigured, the zone is
recreated. To remove it permanently, it must also be removed from
named.conf.
See also rndcaddzone and rndcmodzone.
dnssec ( -status | -rollover-key id [-algalgorithm] [-whentime] | -checkds [-keyid [-algalgorithm]] [-whentime] ( published | withdrawn )) zone [class [view]]
This command allows you to interact with the “dnssec-policy” of a given
zone.
rndcdnssec-status show the DNSSEC signing state for the specified
zone.
rndcdnssec-rollover allows you to schedule key rollover for a
specific key (overriding the original key lifetime).
rndcdnssec-checkds informs named that the DS for
a specified zone’s key-signing key has been confirmed to be published
in, or withdrawn from, the parent zone. This is required in order to
complete a KSK rollover. The -keyid and -algalgorithm arguments
can be used to specify a particular KSK, if necessary; if there is only
one key acting as a KSK for the zone, these arguments can be omitted.
The time of publication or withdrawal for the DS is set to the current
time by default, but can be overridden to a specific time with the
argument -whentime, where time is expressed in YYYYMMDDHHMMSS
notation.
dnstap ( -reopen | -roll [number] )
This command closes and re-opens DNSTAP output files. rndcdnstap-reopen allows
the output file to be renamed externally, so that named can
truncate and re-open it. rndcdnstap-roll causes the output file
to be rolled automatically, similar to log files. The most recent
output file has “.0” appended to its name; the previous most recent
output file is moved to “.1”, and so on. If number is specified, then
the number of backup log files is limited to that number.
This command dumps the server’s caches (default) and/or zones to the dump file for
the specified views. If no view is specified, all views are dumped.
(See the dump-file option in the BIND 9 Administrator Reference
Manual.)
flush
This command flushes the server’s cache.
flushnamename [view]
This command flushes the given name from the view’s DNS cache and, if applicable,
from the view’s nameserver address database, bad server cache, and
SERVFAIL cache.
flushtreename [view]
This command flushes the given name, and all of its subdomains, from the view’s
DNS cache, address database, bad server cache, and SERVFAIL cache.
freeze [zone [class [view]]]
This command suspends updates to a dynamic zone. If no zone is specified, then all
zones are suspended. This allows manual edits to be made to a zone
normally updated by dynamic update, and causes changes in the
journal file to be synced into the master file. All dynamic update
attempts are refused while the zone is frozen.
See also rndcthaw.
halt [-p]
This command stops the server immediately. Recent changes made through dynamic
update or IXFR are not saved to the master files, but are rolled
forward from the journal files when the server is restarted. If
-p is specified, named’s process ID is returned. This allows
an external process to determine when named has completed
halting.
See also rndcstop.
loadkeys [zone [class [view]]]
This command fetches all DNSSEC keys for the given zone from the key directory. If
they are within their publication period, they are merged into the
zone’s DNSKEY RRset. Unlike rndcsign, however, the zone is not
immediately re-signed by the new keys, but is allowed to
incrementally re-sign over time.
This command requires that the zone be configured with a dnssec-policy, or
that the auto-dnssec zone option be set to maintain, and also requires the
zone to be configured to allow dynamic DNS. (See “Dynamic Update Policies” in
the Administrator Reference Manual for more details.)
This command inspects and controls the “managed-keys” database which handles
RFC 5011 DNSSEC trust anchor maintenance. If a view is specified, these
commands are applied to that view; otherwise, they are applied to all
views.
When run with the status keyword, this prints the current status of
the managed-keys database.
When run with the refresh keyword, this forces an immediate refresh
query to be sent for all the managed keys, updating the
managed-keys database if any new keys are found, without waiting
the normal refresh interval.
When run with the sync keyword, this forces an immediate dump of
the managed-keys database to disk (in the file
managed-keys.bind or (viewname.mkeys). This synchronizes
the database with its journal file, so that the database’s current
contents can be inspected visually.
When run with the destroy keyword, the managed-keys database
is shut down and deleted, and all key maintenance is terminated.
This command should be used only with extreme caution.
Existing keys that are already trusted are not deleted from
memory; DNSSEC validation can continue after this command is used.
However, key maintenance operations cease until named is
restarted or reconfigured, and all existing key maintenance states
are deleted.
Running rndcreconfig or restarting named immediately
after this command causes key maintenance to be reinitialized
from scratch, just as if the server were being started for the
first time. This is primarily intended for testing, but it may
also be used, for example, to jumpstart the acquisition of new
keys in the event of a trust anchor rollover, or as a brute-force
repair for key maintenance problems.
modzonezone [class [view]] configuration
This command modifies the configuration of a zone while the server is running. This
command requires the allow-new-zones option to be set to yes.
As with addzone, the configuration string specified on the
command line is the zone configuration text that would ordinarily be
placed in named.conf.
If the zone was originally added via rndcaddzone, the
configuration changes are recorded permanently and are still
in effect after the server is restarted or reconfigured. However, if
it was originally configured in named.conf, then that original
configuration remains in place; when the server is restarted or
reconfigured, the zone reverts to its original configuration. To
make the changes permanent, it must also be modified in
named.conf.
See also rndcaddzone and rndcdelzone.
notifyzone [class [view]]
This command resends NOTIFY messages for the zone.
notrace
This command sets the server’s debugging level to 0.
This command sets a DNSSEC negative trust anchor (NTA) for domain, with a
lifetime of duration. The default lifetime is configured in
named.conf via the nta-lifetime option, and defaults to one
hour. The lifetime cannot exceed one week.
A negative trust anchor selectively disables DNSSEC validation for
zones that are known to be failing because of misconfiguration rather
than an attack. When data to be validated is at or below an active
NTA (and above any other configured trust anchors), named
aborts the DNSSEC validation process and treats the data as insecure
rather than bogus. This continues until the NTA’s lifetime has
elapsed.
NTAs persist across restarts of the named server. The NTAs for a
view are saved in a file called name.nta, where name is the name
of the view; if it contains characters that are incompatible with
use as a file name, a cryptographic hash is generated from the name of
the view.
An existing NTA can be removed by using the -remove option.
An NTA’s lifetime can be specified with the -lifetime option.
TTL-style suffixes can be used to specify the lifetime in seconds,
minutes, or hours. If the specified NTA already exists, its lifetime
is updated to the new value. Setting lifetime to zero is
equivalent to -remove.
If -dump is used, any other arguments are ignored and a list
of existing NTAs is printed. Note that this may include NTAs that are
expired but have not yet been cleaned up.
Normally, named periodically tests to see whether data below
an NTA can now be validated (see the nta-recheck option in the
Administrator Reference Manual for details). If data can be
validated, then the NTA is regarded as no longer necessary and is
allowed to expire early. The -force parameter overrides this behavior
and forces an NTA to persist for its entire lifetime, regardless of
whether data could be validated if the NTA were not present.
The view class can be specified with -class. The default is class
IN, which is the only class for which DNSSEC is currently
supported.
All of these options can be shortened, i.e., to -l, -r,
-d, -f, and -c.
Unrecognized options are treated as errors. To refer to a domain or
view name that begins with a hyphen, use a double-hyphen (–) on the
command line to indicate the end of options.
querylog [(on | off)]
This command enables or disables query logging. For backward compatibility, this
command can also be used without an argument to toggle query logging
on and off.
Query logging can also be enabled by explicitly directing the
queriescategory to a channel in the logging section
of named.conf, or by specifying querylogyes; in the
options section of named.conf.
reconfig
This command reloads the configuration file and loads new zones, but does not reload
existing zone files even if they have changed. This is faster than a
full reload when there is a large number of zones, because it
avoids the need to examine the modification times of the zone files.
recursing
This command dumps the list of queries named is currently
recursing on, and the list of domains to which iterative queries
are currently being sent.
The first list includes all unique clients that are waiting for
recursion to complete, including the query that is awaiting a
response and the timestamp (seconds since the Unix epoch) of
when named started processing this client query.
The second list comprises of domains for which there are active
(or recently active) fetches in progress. It reports the number
of active fetches for each domain and the number of queries that
have been passed (allowed) or dropped (spilled) as a result of
the fetches-per-zone limit. (Note: these counters are not
cumulative over time; whenever the number of active fetches for
a domain drops to zero, the counter for that domain is deleted,
and the next time a fetch is sent to that domain, it is recreated
with the counters set to zero).
refreshzone [class [view]]
This command schedules zone maintenance for the given zone.
reload
This command reloads the configuration file and zones.
reloadzone [class [view]]
This command reloads the given zone.
retransferzone [class [view]]
This command retransfers the given secondary zone from the primary server.
If the zone is configured to use inline-signing, the signed
version of the zone is discarded; after the retransfer of the
unsigned version is complete, the signed version is regenerated
with new signatures.
scan
This command scans the list of available network interfaces for changes, without
performing a full reconfig or waiting for the
interface-interval timer.
secroots [-] [view …]
This command dumps the security roots (i.e., trust anchors configured via
trust-anchors, or the managed-keys or trusted-keys statements
[both deprecated], or dnssec-validationauto) and negative trust anchors
for the specified views. If no view is specified, all views are
dumped. Security roots indicate whether they are configured as trusted
keys, managed keys, or initializing managed keys (managed keys that have not
yet been updated by a successful key refresh query).
If the first argument is -, then the output is returned via the
rndc response channel and printed to the standard output.
Otherwise, it is written to the secroots dump file, which defaults to
named.secroots, but can be overridden via the secroots-file
option in named.conf.
See also rndcmanaged-keys.
serve-stale (on | off | reset | status) [class [view]]
This command enables, disables, resets, or reports the current status of the serving
of stale answers as configured in named.conf.
If serving of stale answers is disabled by rndc-serve-staleoff,
then it remains disabled even if named is reloaded or
reconfigured. rndcserve-stalereset restores the setting as
configured in named.conf.
rndcserve-stalestatus reports whether serving of stale
answers is currently enabled, disabled by the configuration, or
disabled by rndc. It also reports the values of
stale-answer-ttl and max-stale-ttl.
showzonezone [class [view]]
This command prints the configuration of a running zone.
See also rndczonestatus.
signzone [class [view]]
This command fetches all DNSSEC keys for the given zone from the key directory (see
the key-directory option in the BIND 9 Administrator Reference
Manual). If they are within their publication period, they are merged into
the zone’s DNSKEY RRset. If the DNSKEY RRset is changed, then the
zone is automatically re-signed with the new key set.
This command requires that the zone be configured with a dnssec-policy, or
that the auto-dnssec zone option be set to allow or maintain,
and also requires the zone to be configured to allow dynamic DNS. (See
“Dynamic Update Policies” in the BIND 9 Administrator Reference Manual for more
details.)
This command lists, edits, or removes the DNSSEC signing-state records for the
specified zone. The status of ongoing DNSSEC operations, such as
signing or generating NSEC3 chains, is stored in the zone in the form
of DNS resource records of type sig-signing-type.
rndcsigning-list converts these records into a human-readable
form, indicating which keys are currently signing or have finished
signing the zone, and which NSEC3 chains are being created or
removed.
rndcsigning-clear can remove a single key (specified in the
same format that rndcsigning-list uses to display it), or all
keys. In either case, only completed keys are removed; any record
indicating that a key has not yet finished signing the zone is
retained.
rndcsigning-nsec3param sets the NSEC3 parameters for a zone.
This is the only supported mechanism for using NSEC3 with
inline-signing zones. Parameters are specified in the same format
as an NSEC3PARAM resource record: hashalgorithm, flags, iterations,
and salt, in that order.
Currently, the only defined value for hashalgorithm is 1,
representing SHA-1. The flags may be set to 0 or 1,
depending on whether the opt-out bit in the NSEC3
chain should be set. iterations defines the number of additional times to apply
the algorithm when generating an NSEC3 hash. The salt is a string
of data expressed in hexadecimal, a hyphen (-) if no salt is to be
used, or the keyword auto, which causes named to generate a
random 64-bit salt.
The only recommended configuration is rndcsigning-nsec3param100-zone,
i.e. no salt, no additional iterations, no opt-out.
Warning
Do not use extra iterations, salt, or opt-out unless all their implications
are fully understood. A higher number of iterations causes interoperability
problems and opens servers to CPU-exhausting DoS attacks.
rndcsigning-nsec3paramnone removes an existing NSEC3 chain and
replaces it with NSEC.
rndcsigning-serialvalue sets the serial number of the zone to
value. If the value would cause the serial number to go backwards, it
is rejected. The primary use of this parameter is to set the serial number on inline
signed zones.
stats
This command writes server statistics to the statistics file. (See the
statistics-file option in the BIND 9 Administrator Reference
Manual.)
status
This command displays the status of the server. Note that the number of zones includes
the internal bind/CH zone and the default ./IN hint zone, if
there is no explicit root zone configured.
stop-p
This command stops the server, making sure any recent changes made through dynamic
update or IXFR are first saved to the master files of the updated
zones. If -p is specified, named(8)`'sprocessIDisreturned.Thisallowsanexternalprocesstodeterminewhen``named has
completed stopping.
See also rndchalt.
sync-clean [zone [class [view]]]
This command syncs changes in the journal file for a dynamic zone to the master
file. If the “-clean” option is specified, the journal file is also
removed. If no zone is specified, then all zones are synced.
tcp-timeouts [initialidlekeepaliveadvertised]
When called without arguments, this command displays the current values of the
tcp-initial-timeout, tcp-idle-timeout,
tcp-keepalive-timeout, and tcp-advertised-timeout options.
When called with arguments, these values are updated. This allows an
administrator to make rapid adjustments when under a
denial-of-service (DoS) attack. See the descriptions of these options in the BIND 9
Administrator Reference Manual for details of their use.
thaw [zone [class [view]]]
This command enables updates to a frozen dynamic zone. If no zone is specified,
then all frozen zones are enabled. This causes the server to reload
the zone from disk, and re-enables dynamic updates after the load has
completed. After a zone is thawed, dynamic updates are no longer
refused. If the zone has changed and the ixfr-from-differences
option is in use, the journal file is updated to reflect
changes in the zone. Otherwise, if the zone has changed, any existing
journal file is removed.
See also rndcfreeze.
trace
This command increments the server’s debugging level by one.
tracelevel
This command sets the server’s debugging level to an explicit value.
See also rndcnotrace.
tsig-deletekeyname [view]
This command deletes a given TKEY-negotiated key from the server. This does not
apply to statically configured TSIG keys.
tsig-list
This command lists the names of all TSIG keys currently configured for use by
named in each view. The list includes both statically configured keys and
dynamic TKEY-negotiated keys.
validation (on | off | status) [view …]``
This command enables, disables, or checks the current status of DNSSEC validation. By
default, validation is enabled.
The cache is flushed when validation is turned on or off to avoid using data
that might differ between states.
zonestatuszone [class [view]]
This command displays the current status of the given zone, including the master
file name and any include files from which it was loaded, when it was
most recently loaded, the current serial number, the number of nodes,
whether the zone supports dynamic updates, whether the zone is DNSSEC
signed, whether it uses automatic DNSSEC key management or inline
signing, and the scheduled refresh or expiry times for the zone.
See also rndcshowzone.
rndc commands that specify zone names, such as reload,
retransfer, or zonestatus, can be ambiguous when applied to zones
of type redirect. Redirect zones are always called ., and can be
confused with zones of type hint or with secondary copies of the root
zone. To specify a redirect zone, use the special zone name
-redirect, without a trailing period. (With a trailing period, this
would specify a zone called “-redirect”.)
tsig-keygen is an utility that generates keys for use in TSIG signing.
The resulting keys can be used, for example, to secure dynamic DNS updates
to a zone, or for the rndc command channel.
A domain name can be specified on the command line to be used as the name
of the generated key. If no name is specified, the default is tsig-key.
This option specifies the algorithm to use for the TSIG key. Available
choices are: hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384,
and hmac-sha512. The default is hmac-sha256. Options are
case-insensitive, and the “hmac-” prefix may be omitted.
-h
This option prints a short summary of options and arguments.
Comment Syntax
The BIND 9 comment syntax allows comments to appear anywhere that whitespace may appear in a BIND configuration file. To appeal to programmers of all kinds, they can be written in the C, C++, or shell/perl style.
Syntax
Definition and Usage
Comments may appear anywhere that whitespace may appear in a BIND configuration file.
C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.
C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with the first */:
C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use the // pair. For example:
Shell-style (or perl-style) comments start with the character
#(number sign) and continue to the end of the physical line, as in C++ comments. For example:Warning
The semicolon (
;) character cannot start a comment, unlike in a zone file. The semicolon indicates the end of a configuration statement.