General DNS Reference Information

IPv6 Addresses (AAAA)

IPv6 addresses are 128-bit identifiers, for interfaces and sets of interfaces, which were introduced in the DNS to facilitate scalable Internet routing. There are three types of addresses: Unicast, an identifier for a single interface; Anycast, an identifier for a set of interfaces; and Multicast, an identifier for a set of interfaces. Here we describe the global Unicast address scheme. For more information, see RFC 3587, “IPv6 Global Unicast Address Format.”

IPv6 unicast addresses consist of a global routing prefix, a subnet identifier, and an interface identifier.

The global routing prefix is provided by the upstream provider or ISP, and roughly corresponds to the IPv4 network section of the address range. The subnet identifier is for local subnetting, much like subnetting an IPv4 /16 network into /24 subnets. The interface identifier is the address of an individual interface on a given network; in IPv6, addresses belong to interfaces rather than to machines.

The subnetting capability of IPv6 is much more flexible than that of IPv4: subnetting can be carried out on bit boundaries, in much the same way as Classless InterDomain Routing (CIDR), and the DNS PTR representation (“nibble” format) makes setting up reverse zones easier.

The interface identifier must be unique on the local link, and is usually generated automatically by the IPv6 implementation, although it is usually possible to override the default setting if necessary. A typical IPv6 address might look like: 2001:db8:201:9:a00:20ff:fe81:2b32

IPv6 address specifications often contain long strings of zeros, so the architects have included a shorthand for specifying them. The double colon (::) indicates the longest possible string of zeros that can fit, and can be used only once in an address.

Bibliography (and Suggested Reading)

Request for Comments (RFCs)

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.

Specification documents for the Internet protocol suite, including the DNS, are published as part of the Request for Comments (RFCs) series of technical notes. The standards themselves are defined by the Internet Engineering Task Force (IETF) and the Internet Engineering Steering Group (IESG). RFCs can be viewed online at:

Some of these RFCs, though DNS-related, are not concerned with implementing software.

Internet Standards

RFC 1034 - P. Mockapetris. Domain Names — Concepts and Facilities. November 1987.

RFC 1035 - P. Mockapetris. Domain Names — Implementation and Specification. November 1987. [1] [2]

RFC 1123 - R. Braden. Requirements for Internet Hosts - Application and Support. October 1989.

RFC 3596 - S. Thomson, C. Huitema, V. Ksinant, and M. Souissi. DNS Extensions to Support IP Version 6. October 2003.

RFC 5011 - M. StJohns. Automated Updates of DNS Security (DNSSEC) Trust Anchors.

RFC 6891 - J. Damas, M. Graff, and P. Vixie. Extension Mechanisms for DNS (EDNS(0)). April 2013.

Proposed Standards

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 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 2845 - P. Vixie, O. Gudmundsson, D. Eastlake, 3rd, and B. Wellington. Secret Key Transaction Authentication for DNS (TSIG). May 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 3226 - O. Gudmundsson. DNSSEC and IPv6 A6 Aware Server/Resolver Message Size Requirements. December 2001.

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 3225 - D. Conrad. Indicating Resolver Support of DNSSEC. December 2001.

RFC 3492 - A. Costello. Punycode: A Bootstring Encoding of Unicode for Internationalized Domain Names in Applications (IDNA). March 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. [4]

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. [5]

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. [6]

RFC 5001 - R. Austein. DNS Name Server Identifier (NSID) Option. August 2007.

RFC 5155 - B. Laurie, G. Sisson, R. Arends, and D. Blacka. DNS Security (DNSSEC) Hashed Authenticated Denial of Existence. March 2008.

RFC 5452 - A. Hubert and R. van Mook. Measures for Making DNS More Resilient Against Forged Answers. January 2009. [7]

RFC 5702 - J. Jansen. Use of SHA-2 Algorithms with RSA in DNSKEY and RRSIG Resource Records for DNSSEC. October 2009.

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. [8]

RFC 6594 - O. Sury. Use of the SHA-256 Algorithm with RSA, Digital Signature Algorithm (DSA), and Elliptic Curve DSA (ECDSA) in SSHFP Resource Records. April 2012.

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. [9]

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. [10]

RFC 6840 - S. Weiler, Ed., and D. Blacka, Ed. Clarifications and Implementation Notes for DNS Security (DNSSEC). February 2013. [11]

RFC 7216 - M. Thomson and R. Bellis. Location Information Server (LIS) Discovery Using IP Addresses and Reverse DNS. April 2014.

RFC 7344 - W. Kumari, O. Gudmundsson, and G. Barwood. Automating DNSSEC Delegation Trust Maintenance. September 2014. [12]

RFC 7477 - W. Hardaker. Child-to-Parent Synchronization in DNS. March 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. [13]

RFC 8080 - O. Sury and R. Edmonds. Edwards-Curve Digital Security Algorithm (EdDSA) for DNSSEC. February 2017.

RFC 8482 - J. Abley, O. Gudmundsson, M. Majkowski, and E. Hunt. Providing Minimal-Sized Responses to DNS Queries That Have QTYPE=ANY. January 2019.

RFC 8490 - R. Bellis, S. Cheshire, J. Dickinson, S. Dickinson, T. Lemon, and T. Pusateri. DNS Stateful Operations. March 2019.

RFC 8624 - P. Wouters and O. Sury. Algorithm Implementation Requirements and Usage Guidance for DNSSEC. June 2019.

RFC 8749 - W. Mekking and D. Mahoney. Moving DNSSEC Lookaside Validation (DLV) to Historic Status. March 2020.

Informational RFCs

RFC 1535 - E. Gavron. A Security Problem and Proposed Correction With Widely Deployed DNS Software. October 1993.

RFC 1536 - A. Kumar, J. Postel, C. Neuman, P. Danzig, and S. Miller. Common DNS Implementation Errors and Suggested Fixes. October 1993.

RFC 1591 - J. Postel. Domain Name System Structure and Delegation. March 1994.

RFC 1706 - B. Manning and R. Colella. DNS NSAP Resource Records. October 1994.

RFC 1713 - A. Romao. Tools for DNS Debugging. November 1994.

RFC 1794 - T. Brisco. DNS Support for Load Balancing. April 1995.

RFC 1912 - D. Barr. Common DNS Operational and Configuration Errors. February 1996.

RFC 2230 - R. Atkinson. Key Exchange Delegation Record for the DNS. November 1997.

RFC 2352 - O. Vaughan. A Convention for Using Legal Names as Domain Names. May 1998.

RFC 2825 - IAB and L. Daigle. A Tangled Web: Issues of I18N, Domain Names, and the Other Internet Protocols. May 2000.

RFC 2826 - Internet Architecture Board. IAB Technical Comment on the Unique DNS Root. May 2000.

RFC 3071 - J. Klensin. Reflections on the DNS, RFC 1591, and Categories of Domains. February 2001.

RFC 3258 - T. Hardie. Distributing Authoritative Name Servers via Shared Unicast Addresses. April 2002.

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. [14]

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 3833 - D. Atkins and R. Austein. Threat Analysis of the Domain Name System (DNS). August 2004.

RFC 4074 - Y. Morishita and T. Jinmei. Common Misbehavior Against DNS Queries for IPv6 Addresses. June 2005.

RFC 4892 - S. Woolf and D. Conrad. Requirements for a Mechanism Identifying a Name Server Instance. June 2007.

RFC 6781 - O. Kolkman, W. Mekking, and R. Gieben. DNSSEC Operational Practices, Version 2. December 2012.

RFC 7043 - J. Abley. Resource Records for EUI-48 and EUI-64 Addresses in the DNS. October 2013.

RFC 7129 - R. Gieben and W. Mekking. Authenticated Denial of Existence in the DNS. February 2014.

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.

Experimental RFCs

RFC 1183 - C. F. Everhart, L. A. Mamakos, R. Ullmann, P. Mockapetris. New DNS RR Definitions. October 1990.

RFC 1464 - R. Rosenbaum. Using the Domain Name System to Store Arbitrary String Attributes. May 1993.

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 2345 - J. Klensin, T. Wolf, and G. Oglesby. Domain Names and Company Name Retrieval. May 1998.

RFC 2540 - D. Eastlake, 3rd. Detached Domain Name System (DNS) Information. March 1999.

RFC 3123 - P. Koch. A DNS RR Type for Lists of Address Prefixes (APL RR). June 2001.

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 7314 - M. Andrews. Extension Mechanisms for DNS (EDNS) EXPIRE Option. July 2014.

RFC 7929 - P. Wouters. DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP. August 2016.

Best Current Practice RFCs

RFC 2219 - M. Hamilton and R. Wright. Use of DNS Aliases for Network Services. October 1997.

RFC 2317 - H. Eidnes, G. de Groot, and P. Vixie. Classless IN-ADDR.ARPA Delegation. March 1998.

RFC 2606 - D. Eastlake, 3rd and A. Panitz. Reserved Top Level DNS Names. June 1999. [15]

RFC 3901 - A. Durand and J. Ihren. DNS IPv6 Transport Operational Guidelines. September 2004.

RFC 5625 - R. Bellis. DNS Proxy Implementation Guidelines. August 2009.

RFC 6303 - M. Andrews. Locally Served DNS Zones. July 2011.

RFC 7793 - M. Andrews. Adding Prefixes to the IPv4 Locally-Served DNS Zones Registry. May 2016.

Historic RFCs

RFC 2874 - M. Crawford and C. Huitema. DNS Extensions to Support IPv6 Address Aggregation and Renumbering. July 2000. [4]

RFC 4431 - M. Andrews and S. Weiler. The DNSSEC Lookaside Validation (DLV) DNS Resource Record. February 2006.

RFCs of Type “Unknown”

RFC 1033 - M. Lottor. Domain Administrators Operations Guide. November 1987.

RFC 1101 - P. Mockapetris. DNS Encoding of Network Names and Other Types. April 1989.

Obsoleted and Unimplemented Experimental RFCs

RFC 974 - C. Partridge. Mail Routing and the Domain System. January 1986.

RFC 1521 - N. Borenstein and N. Freed. MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies. September 1993 [16]

RFC 1537 - P. Beertema. Common DNS Data File Configuration Errors. October 1993.

RFC 1750 - D. Eastlake, 3rd, S. Crocker, and J. Schiller. Randomness Recommendations for Security. December 1994.

RFC 2010 - B. Manning and P. Vixie. Operational Criteria for Root Name Servers. October 1996.

RFC 2052 - A. Gulbrandsen and P. Vixie. A DNS RR for Specifying the Location of Services. October 1996.

RFC 2065 - D. Eastlake, 3rd and C. Kaufman. Domain Name System Security Extensions. January 1997.

RFC 2137 - D. Eastlake, 3rd. Secure Domain Name System Dynamic Update. April 1997.

RFC 2168 - R. Daniel and M. Mealling. Resolution of Uniform Resource Identifiers Using the Domain Name System. June 1997.

RFC 2240 - O. Vaughan. A Legal Basis for Domain Name Allocation. November 1997.

RFC 2535 - D. Eastlake, 3rd. Domain Name System Security Extensions. March 1999. [17] [18]

RFC 2537 - D. Eastlake, 3rd. RSA/MD5 KEYs and SIGs in the Domain Name System (DNS). March 1999.

RFC 2538 - D. Eastlake, 3rd and O. Gudmundsson. Storing Certificates in the Domain Name System (DNS). March 1999.

RFC 2671 - P. Vixie. Extension Mechanisms for DNS (EDNS0). August 1999.

RFC 2672 - M. Crawford. Non-Terminal DNS Name Redirection. August 1999.

RFC 2673 - M. Crawford. Binary Labels in the Domain Name System. August 1999.

RFC 2915 - M. Mealling and R. Daniel. The Naming Authority Pointer (NAPTR) DNS Resource Record. September 2000.

RFC 2929 - D. Eastlake, 3rd, E. Brunner-Williams, and B. Manning. Domain Name System (DNS) IANA Considerations. September 2000.

RFC 3008 - B. Wellington. Domain Name System Security (DNSSEC) Signing Authority. November 2000.

RFC 3090 - E. Lewis. DNS Security Extension Clarification on Zone Status. March 2001.

RFC 3152 - R. Bush. Delegation of IP6.ARPA. August 2001.

RFC 3445 - D. Massey and S. Rose. Limiting the Scope of the KEY Resource Record (RR). December 2002.

RFC 3490 - P. Faltstrom, P. Hoffman, and A. Costello. Internationalizing Domain Names in Applications (IDNA). March 2003. [19]

RFC 3491 - P. Hoffman and M. Blanchet. Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN). March 2003. [19]

RFC 3655 - B. Wellington and O. Gudmundsson. Redefinition of DNS Authenticated Data (AD) Bit. November 2003.

RFC 3658 - O. Gudmundsson. Delegation Signer (DS) Resource Record (RR). December 2003.

RFC 3755 - S. Weiler. Legacy Resolver Compatibility for Delegation Signer (DS). May 2004.

RFC 3757 - O. Kolkman, J. Schlyter, and E. Lewis. Domain Name System KEY (DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag. May 2004.

RFC 3845 - J. Schlyter. DNS Security (DNSSEC) NextSECure (NSEC) RDATA Format. August 2004.

RFC 4294 - J. Loughney, Ed. IPv6 Node Requirements. [20]

RFC 4408 - M. Wong and W. Schlitt. Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1. April 2006.

RFC 5966 - R. Bellis. DNS Transport Over TCP - Implementation Requirements. August 2010.

RFC 6844 - P. Hallam-Baker and R. Stradling. DNS Certification Authority Authorization (CAA) Resource Record. January 2013.

RFC 6944 - S. Rose. Applicability Statement: DNS Security (DNSSEC) DNSKEY Algorithm Implementation Status. April 2013.

RFCs No Longer Supported in BIND 9

RFC 2536 - D. Eastlake, 3rd. DSA KEYs and SIGs in the Domain Name System (DNS). March 1999.

[1] Queries to zones that have failed to load return SERVFAIL rather than a non-authoritative response. This is considered a feature.

[2] CLASS ANY queries are not supported. This is considered a feature.

[3] 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.

[4] Compliance is with loading and serving of A6 records only. A6 records were moved to the experimental category by RFC 3363.

[5] Minimally covering NSEC records are accepted but not generated.

[6] BIND 9 interoperates with correctly designed experiments.

[7] named only uses ports to extend the ID space; addresses are not used.

[8] 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.

[9] Compliance is conditional on the OpenSSL library being linked against a supporting ECDSA.

[10] RSAMD5 support has been removed. See RFC 6944.

[11] 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.

[12] Updating of parent zones is not yet implemented.

[13] ``named` does not currently encrypt DNS requests, so the PAD option is accepted but not returned in responses.

[14] Section 4 is ignored.

[15] This does not apply to DNS server implementations.

[16] Only the Base 64 encoding specification is supported.

[17] Wildcard records are not supported in DNSSEC secure zones.

[18] Servers authoritative for secure zones being resolved by BIND 9 must support EDNS0 (RFC2671), and must return all relevant SIGs and NXTs in responses, rather than relying on the resolving server to perform separate queries for missing SIGs and NXTs.

[19] BIND 9 requires --with-idn to enable entry of IDN labels within dig, host, and nslookup at compile time. ACE labels are supported everywhere with or without --with-idn.

[20] Section 5.1 - DNAME records are fully supported.

Internet Drafts

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.

Other Documents About BIND

Paul Albitz and Cricket Liu. DNS and BIND. Copyright 1998 Sebastopol, CA: O’Reilly and Associates.