7Network Working Group R. Bush
8Request for Comments: 3363 A. Durand
9Updates: 2673, 2874 B. Fink
10Category: Informational O. Gudmundsson
16 Representing Internet Protocol version 6 (IPv6)
17 Addresses in the Domain Name System (DNS)
21 This memo provides information for the Internet community. It does
22 not specify an Internet standard of any kind. Distribution of this
27 Copyright (C) The Internet Society (2002). All Rights Reserved.
31 This document clarifies and updates the standards status of RFCs that
32 define direct and reverse map of IPv6 addresses in DNS. This
33 document moves the A6 and Bit label specifications to experimental
38 The IETF had begun the process of standardizing two different address
39 formats for IPv6 addresses AAAA [RFC1886] and A6 [RFC2874] and both
40 are at proposed standard. This had led to confusion and conflicts on
41 which one to deploy. It is important for deployment that any
42 confusion in this area be cleared up, as there is a feeling in the
43 community that having more than one choice will lead to delays in the
44 deployment of IPv6. The goal of this document is to clarify the
47 This document also discusses issues relating to the usage of Binary
48 Labels [RFC 2673] to support the reverse mapping of IPv6 addresses.
50 This document is based on extensive technical discussion on various
51 relevant working groups mailing lists and a joint DNSEXT and NGTRANS
52 meeting at the 51st IETF in August 2001. This document attempts to
53 capture the sense of the discussions and reflect them in this
54 document to represent the consensus of the community.
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60RFC 3363 Representation of IPv6 Addresses in DNS August 2002
63 The main arguments and the issues are covered in a separate document
64 [RFC3364] that reflects the current understanding of the issues.
65 This document summarizes the outcome of these discussions.
67 The issue of the root of reverse IPv6 address map is outside the
68 scope of this document and is covered in a different document
711.1 Standards Action Taken
73 This document changes the status of RFCs 2673 and 2874 from Proposed
74 Standard to Experimental.
762. IPv6 Addresses: AAAA RR vs A6 RR
78 Working group consensus as perceived by the chairs of the DNSEXT and
79 NGTRANS working groups is that:
81 a) AAAA records are preferable at the moment for production
82 deployment of IPv6, and
84 b) that A6 records have interesting properties that need to be better
85 understood before deployment.
87 c) It is not known if the benefits of A6 outweigh the costs and
92 There are several potential issues with A6 RRs that stem directly
93 from the feature that makes them different from AAAA RRs: the ability
94 to build up addresses via chaining.
96 Resolving a chain of A6 RRs involves resolving a series of what are
97 nearly-independent queries. Each of these sub-queries takes some
98 non-zero amount of time, unless the answer happens to be in the
99 resolver's local cache already. Other things being equal, we expect
100 that the time it takes to resolve an N-link chain of A6 RRs will be
101 roughly proportional to N. What data we have suggests that users are
102 already impatient with the length of time it takes to resolve A RRs
103 in the IPv4 Internet, which suggests that users are not likely to be
104 patient with significantly longer delays in the IPv6 Internet, but
105 terminating queries prematurely is both a waste of resources and
106 another source of user frustration. Thus, we are forced to conclude
107 that indiscriminate use of long A6 chains is likely to lead to
108 increased user frustration.
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116RFC 3363 Representation of IPv6 Addresses in DNS August 2002
119 The probability of failure during the process of resolving an N-link
120 A6 chain also appears to be roughly proportional to N, since each of
121 the queries involved in resolving an A6 chain has roughly the same
122 probability of failure as a single AAAA query.
124 Last, several of the most interesting potential applications for A6
125 RRs involve situations where the prefix name field in the A6 RR
126 points to a target that is not only outside the DNS zone containing
127 the A6 RR, but is administered by a different organization entirely.
128 While pointers out of zone are not a problem per se, experience both
129 with glue RRs and with PTR RRs in the IN-ADDR.ARPA tree suggests that
130 pointers to other organizations are often not maintained properly,
131 perhaps because they're less susceptible to automation than pointers
132 within a single organization would be.
1342.2 Recommended Standard Action
136 Based on the perceived consensus, this document recommends that RFC
137 1886 stay on standards track and be advanced, while moving RFC 2874
138 to Experimental status.
1403. Bitlabels in the Reverse DNS Tree
142 RFC 2673 defines a new DNS label type. This was the first new type
143 defined since RFC 1035 [RFC1035]. Since the development of 2673 it
144 has been learned that deployment of a new type is difficult since DNS
145 servers that do not support bitlabels reject queries containing bit
146 labels as being malformed. The community has also indicated that
147 this new label type is not needed for mapping reverse addresses.
151 The hexadecimal text representation of IPv6 addresses appears to be
152 capable of expressing all of the delegation schemes that we expect to
153 be used in the DNS reverse tree.
1553.2 Recommended Standard Action
157 RFC 2673 standard status is to be changed from Proposed to
158 Experimental. Future standardization of these documents is to be
159 done by the DNSEXT working group or its successor.
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172RFC 3363 Representation of IPv6 Addresses in DNS August 2002
1754. DNAME in IPv6 Reverse Tree
177 The issues for DNAME in the reverse mapping tree appears to be
178 closely tied to the need to use fragmented A6 in the main tree: if
179 one is necessary, so is the other, and if one isn't necessary, the
180 other isn't either. Therefore, in moving RFC 2874 to experimental,
181 the intent of this document is that use of DNAME RRs in the reverse
186 This document is based on input from many members of the various IETF
187 working groups involved in this issues. Special thanks go to the
188 people that prepared reading material for the joint DNSEXT and
189 NGTRANS working group meeting at the 51st IETF in London, Rob
190 Austein, Dan Bernstein, Matt Crawford, Jun-ichiro itojun Hagino,
191 Christian Huitema. Number of other people have made number of
192 comments on mailing lists about this issue including Andrew W.
193 Barclay, Robert Elz, Johan Ihren, Edward Lewis, Bill Manning, Pekka
1966. Security Considerations
198 As this document specifies a course of action, there are no direct
199 security considerations. There is an indirect security impact of the
200 choice, in that the relationship between A6 and DNSSEC is not well
201 understood throughout the community, while the choice of AAAA does
202 leads to a model for use of DNSSEC in IPv6 networks which parallels
203 current IPv4 practice.
2057. IANA Considerations
211 [RFC1035] Mockapetris, P., "Domain Names - Implementation and
212 Specification", STD 13, RFC 1035, November 1987.
214 [RFC1886] Thompson, S. and C. Huitema, "DNS Extensions to support IP
215 version 6", RFC 1886, December 1995.
217 [RFC2673] Crawford, M., "Binary Labels in the Domain Name System",
218 RFC 2673, August 1999.
220 [RFC2874] Crawford, M. and C. Huitema, "DNS Extensions to Support
221 IPv6 Address Aggregation and Renumbering", RFC 2874, July
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228RFC 3363 Representation of IPv6 Addresses in DNS August 2002
231 [RFC3152] Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152
234Informative References
236 [RFC3364] Austein, R., "Tradeoffs in Domain Name System (DNS)
237 Support for Internet Protocol version 6 (IPv6)", RFC 3364,
247 EMail: alain.durand@sun.com
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287Full Copyright Statement
289 Copyright (C) The Internet Society (2002). All Rights Reserved.
291 This document and translations of it may be copied and furnished to
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