DNS IPv6 Extensions: DNS Extensions to Support IP Version 6
How the Domain Name System first learned to store and look up IPv6 addresses.
Thomson, S. and C. Huitema, "DNS Extensions to support IP version 6", RFC 1886, DOI 10.17487/RFC1886, December 1995, <https://www.rfc-editor.org/info/rfc1886>.
@misc{rfc1886,
series = {Request for Comments},
number = 1886,
howpublished = {RFC 1886},
publisher = {RFC Editor},
doi = {10.17487/RFC1886},
url = {https://www.rfc-editor.org/info/rfc1886},
author = {S. Thomson and C. Huitema},
title = {{DNS Extensions to support IP version 6}},
pagetotal = 5,
year = 1995,
month = dec,
} RFC text
Contents
Network Working Group S. Thomson
Request for Comments: 1886 Bellcore
Category: Standards Track C. Huitema
INRIA
December 1995
DNS Extensions to support IP version 6
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines the changes that need to be made to the Domain
Name System to support hosts running IP version 6 (IPv6). The
changes include a new resource record type to store an IPv6 address,
a new domain to support lookups based on an IPv6 address, and updated
definitions of existing query types that return Internet addresses as
part of additional section processing. The extensions are designed
to be compatible with existing applications and, in particular, DNS
implementations themselves.
1. INTRODUCTION
Current support for the storage of Internet addresses in the Domain
Name System (DNS)[1,2] cannot easily be extended to support IPv6
addresses[3] since applications assume that address queries return
32-bit IPv4 addresses only.
To support the storage of IPv6 addresses we define the following
extensions:
o A new resource record type is defined to map a domain name to an
IPv6 address.
o A new domain is defined to support lookups based on address.
o Existing queries that perform additional section processing to
locate IPv4 addresses are redefined to perform additional
section processing on both IPv4 and IPv6 addresses.
The changes are designed to be compatible with existing software. The
existing support for IPv4 addresses is retained. Transition issues
related to the co-existence of both IPv4 and IPv6 addresses in DNS
are discussed in [4].
2. NEW RESOURCE RECORD DEFINITION AND DOMAIN
A new record type is defined to store a host's IPv6 address. A host
that has more than one IPv6 address must have more than one such
record.
2.1 AAAA record type
The AAAA resource record type is a new record specific to the
Internet class that stores a single IPv6 address.
The value of the type is 28 (decimal).
2.2 AAAA data format
A 128 bit IPv6 address is encoded in the data portion of an AAAA
resource record in network byte order (high-order byte first).
2.3 AAAA query
An AAAA query for a specified domain name in the Internet class
returns all associated AAAA resource records in the answer section of
a response.
A type AAAA query does not perform additional section processing.
2.4 Textual format of AAAA records
The textual representation of the data portion of the AAAA resource
record used in a master database file is the textual representation
of a IPv6 address as defined in [3].
2.5 IP6.INT Domain
A special domain is defined to look up a record given an address. The
intent of this domain is to provide a way of mapping an IPv6 address
to a host name, although it may be used for other purposes as well.
The domain is rooted at IP6.INT.
An IPv6 address is represented as a name in the IP6.INT domain by a
sequence of nibbles separated by dots with the suffix ".IP6.INT". The
sequence of nibbles is encoded in reverse order, i.e. the low-order
nibble is encoded first, followed by the next low-order nibble and so
on. Each nibble is represented by a hexadecimal digit. For example,
the inverse lookup domain name corresponding to the address
4321:0:1:2:3:4:567:89ab
would be
b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.INT.
3. MODIFICATIONS TO EXISTING QUERY TYPES
All existing query types that perform type A additional section
processing, i.e. name server (NS), mail exchange (MX) and mailbox
(MB) query types, must be redefined to perform both type A and type
AAAA additional section processing. These new definitions mean that a
name server must add any relevant IPv4 addresses and any relevant
IPv6 addresses available locally to the additional section of a
response when processing any one of the above queries.
4. SECURITY CONSIDERATIONS
Security issues are not discussed in this memo.
5. REFERENCES
[1] Mockapetris, P., "Domain Names - Concepts and Facilities", STD
13, RFC 1034, USC/Information Sciences Institute, November 1987.
[2] Mockapetris, P., "Domain Names - Implementation and Specifica-
tion", STD 13, RFC 1035, USC/Information Sciences Institute,
November 1987.
[3] Hinden, R., and S. Deering, Editors, "IP Version 6 Addressing
Architecture", RFC 1884, Ipsilon Networks, Xerox PARC, December
1995.
[4] Gilligan, R., and E. Nordmark, "Transition Mechanisms for IPv6
Hosts and Routers", Work in Progress.
Authors' Addresses
Susan Thomson
Bellcore
MRE 2P343
445 South Street
Morristown, NJ 07960
U.S.A.
Phone: +1 201-829-4514
EMail: set@thumper.bellcore.com
Christian Huitema
INRIA, Sophia-Antipolis
2004 Route des Lucioles
BP 109
F-06561 Valbonne Cedex
France
Phone: +33 93 65 77 15
EMail: Christian.Huitema@MIRSA.INRIA.FR
AI ELI5
On this page
§1Why DNS Needed Changes
Existing DNS support for storing Internet addresses cannot easily be extended to IPv6, since applications assume that address queries return 32-bit IPv4 addresses only. This memo defines three extensions: a new resource record type that maps a name to an IPv6 address, a new domain for lookups based on address, and redefined queries that locate both IPv4 and IPv6 addresses in additional section processing.
The changes are designed to be compatible with existing software, and existing IPv4 support is retained. The coexistence of IPv4 and IPv6 in DNS is left to a separate transition document.
The old phone book had boxes sized for short numbers. The new numbers are much longer, so the book needed a new kind of box without breaking the old ones.
§2The AAAA Record
The AAAA resource record type is specific to the Internet class and stores a single IPv6 address. Its type value is 28 (decimal). A host with more than one IPv6 address must have more than one such record.
The 128-bit address is encoded in the data portion in network byte order, high-order byte first. In a master database file, it is written in the textual form of an IPv6 address defined in RFC 1884.
An AAAA query for a domain name in the Internet class returns all associated AAAA records in the answer section. A type AAAA query does not perform additional section processing.
An AAAA entry is one line in the phone book that holds one long new-style number. If a computer has several numbers, it gets several lines.
§3Looking Up a Name from an Address
A special domain rooted at IP6.INT maps an IPv6 address to a host name, although it may be used for other purposes as well. An address becomes a name by writing its nibbles (4-bit hexadecimal digits) in reverse order, low-order nibble first, separated by dots, with the suffix .IP6.INT.
The RFC's example is the address 4321:0:1:2:3:4:567:89ab, whose lookup name is shown below.
To look up who owns a number, you write the number backwards one digit at a time and add a special ending. Then you ask the phone book about that backwards name.
b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.INT.§4Changes to Existing Queries
Existing query types that perform type A additional section processing, namely name server (NS), mail exchange (MX) and mailbox (MB), must be redefined to perform both type A and type AAAA additional section processing.
So when a name server answers one of these queries, it must add any relevant IPv4 addresses and any relevant IPv6 addresses it has locally to the additional section of the response.
The memo says security issues are not discussed in it.
When the phone book tells you where a mail office is, it now also hands you both the old-style and the new-style numbers if it has them.