Network Working Group R. Bush
Request for Comments: 3363 A. Durand
Updates: 2673, 2874 B. Fink
Category: Informational O. Gudmundsson
Representing Internet Protocol version 6 (IPv6)
Addresses in the Domain Name System (DNS)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document clarifies and updates the standards status of RFCs that
define direct and reverse map of IPv6 addresses in DNS. This
document moves the A6 and Bit label specifications to experimental
The IETF had begun the process of standardizing two different address
formats for IPv6 addresses AAAA [RFC1886] and A6 [RFC2874] and both
are at proposed standard. This had led to confusion and conflicts on
which one to deploy. It is important for deployment that any
confusion in this area be cleared up, as there is a feeling in the
community that having more than one choice will lead to delays in the
deployment of IPv6. The goal of this document is to clarify the
This document also discusses issues relating to the usage of Binary
Labels [RFC 2673] to support the reverse mapping of IPv6 addresses.
This document is based on extensive technical discussion on various
relevant working groups mailing lists and a joint DNSEXT and NGTRANS
meeting at the 51st IETF in August 2001. This document attempts to
capture the sense of the discussions and reflect them in this
document to represent the consensus of the community.
Bush, et. al. Informational [Page 1]RFC 3363 Representation of IPv6 Addresses in DNS August 2002
The main arguments and the issues are covered in a separate document
[RFC3364] that reflects the current understanding of the issues.
This document summarizes the outcome of these discussions.
The issue of the root of reverse IPv6 address map is outside the
scope of this document and is covered in a different document
1.1 Standards Action Taken
This document changes the status of RFCs 2673 and 2874 from Proposed
Standard to Experimental.
2. IPv6 Addresses: AAAA RR vs A6 RR
Working group consensus as perceived by the chairs of the DNSEXT and
NGTRANS working groups is that:
a) AAAA records are preferable at the moment for production
deployment of IPv6, and
b) that A6 records have interesting properties that need to be better
understood before deployment.
c) It is not known if the benefits of A6 outweigh the costs and
There are several potential issues with A6 RRs that stem directly
from the feature that makes them different from AAAA RRs: the ability
to build up addresses via chaining.
Resolving a chain of A6 RRs involves resolving a series of what are
nearly-independent queries. Each of these sub-queries takes some
non-zero amount of time, unless the answer happens to be in the
resolver's local cache already. Other things being equal, we expect
that the time it takes to resolve an N-link chain of A6 RRs will be
roughly proportional to N. What data we have suggests that users are
already impatient with the length of time it takes to resolve A RRs
in the IPv4 Internet, which suggests that users are not likely to be
patient with significantly longer delays in the IPv6 Internet, but
terminating queries prematurely is both a waste of resources and
another source of user frustration. Thus, we are forced to conclude
that indiscriminate use of long A6 chains is likely to lead to
increased user frustration.
Bush, et. al. Informational [Page 2]RFC 3363 Representation of IPv6 Addresses in DNS August 2002
The probability of failure during the process of resolving an N-link
A6 chain also appears to be roughly proportional to N, since each of
the queries involved in resolving an A6 chain has roughly the same
probability of failure as a single AAAA query.
Last, several of the most interesting potential applications for A6