Network Working Group S. Thomson
Request for Comments: 1886 Bellcore
Category: Standards Track C. Huitema
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.
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
Current support for the storage of Internet addresses in the Domain
Name System (DNS)[1,2] cannot easily be extended to support IPv6
addresses since applications assume that address queries return
32-bit IPv4 addresses only.
To support the storage of IPv6 addresses we define the following
o A new resource record type is defined to map a domain name to an
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 .
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
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 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 .
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
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
 Mockapetris, P., "Domain Names - Concepts and Facilities", STD
13, RFC 1034, USC/Information Sciences Institute, November 1987.
 Mockapetris, P., "Domain Names - Implementation and Specifica-
tion", STD 13, RFC 1035, USC/Information Sciences Institute,
 Hinden, R., and S. Deering, Editors, "IP Version 6 Addressing
Architecture", RFC 1884, Ipsilon Networks, Xerox PARC, December
 Gilligan, R., and E. Nordmark, "Transition Mechanisms for IPv6
Hosts and Routers", Work in Progress.
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