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+Network Working Group                                            R. Bush
+Request for Comments: 3363                                     A. Durand
+Updates: 2673, 2874                                              B. Fink
+Category: Informational                                   O. Gudmundsson
+                                                                 T. Hain
+                                                                 Editors
+                                                             August 2002
+
+
+            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 Notice
+
+   Copyright (C) The Internet Society (2002).  All Rights Reserved.
+
+Abstract
+
+   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
+   status.
+
+1.  Introduction
+
+   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
+   situation.
+
+   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
+   [RFC3152].
+
+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
+      risks.
+
+2.1 Rationale
+
+   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
+   RRs involve situations where the prefix name field in the A6 RR
+   points to a target that is not only outside the DNS zone containing
+   the A6 RR, but is administered by a different organization entirely.
+   While pointers out of zone are not a problem per se, experience both
+   with glue RRs and with PTR RRs in the IN-ADDR.ARPA tree suggests that
+   pointers to other organizations are often not maintained properly,
+   perhaps because they're less susceptible to automation than pointers
+   within a single organization would be.
+
+2.2 Recommended Standard Action
+
+   Based on the perceived consensus, this document recommends that RFC
+   1886 stay on standards track and be advanced, while moving RFC 2874
+   to Experimental status.
+
+3.  Bitlabels in the Reverse DNS Tree
+
+   RFC 2673 defines a new DNS label type.  This was the first new type
+   defined since RFC 1035 [RFC1035].  Since the development of 2673 it
+   has been learned that deployment of a new type is difficult since DNS
+   servers that do not support bitlabels reject queries containing bit
+   labels as being malformed.  The community has also indicated that
+   this new label type is not needed for mapping reverse addresses.
+
+3.1 Rationale
+
+   The hexadecimal text representation of IPv6 addresses appears to be
+   capable of expressing all of the delegation schemes that we expect to
+   be used in the DNS reverse tree.
+
+3.2 Recommended Standard Action
+
+   RFC 2673 standard status is to be changed from Proposed to
+   Experimental.  Future standardization of these documents is to be
+   done by the DNSEXT working group or its successor.
+
+
+
+
+
+
+
+
+
+
+Bush, et. al.                Informational                      [Page 3]
+
+RFC 3363        Representation of IPv6 Addresses in DNS      August 2002
+
+
+4.  DNAME in IPv6 Reverse Tree
+
+   The issues for DNAME in the reverse mapping tree appears to be
+   closely tied to the need to use fragmented A6 in the main tree: if
+   one is necessary, so is the other, and if one isn't necessary, the
+   other isn't either.  Therefore, in moving RFC 2874 to experimental,
+   the intent of this document is that use of DNAME RRs in the reverse
+   tree be deprecated.
+
+5.  Acknowledgments
+
+   This document is based on input from many members of the various IETF
+   working groups involved in this issues.  Special thanks go to the
+   people that prepared reading material for the joint DNSEXT and
+   NGTRANS working group meeting at the 51st IETF in London, Rob
+   Austein, Dan Bernstein, Matt Crawford, Jun-ichiro itojun Hagino,
+   Christian Huitema.  Number of other people have made number of
+   comments on mailing lists about this issue including Andrew W.
+   Barclay, Robert Elz, Johan Ihren, Edward Lewis, Bill Manning, Pekka
+   Savola, Paul Vixie.
+
+6.  Security Considerations
+
+   As this document specifies a course of action, there are no direct
+   security considerations.  There is an indirect security impact of the
+   choice, in that the relationship between A6 and DNSSEC is not well
+   understood throughout the community, while the choice of AAAA does
+   leads to a model for use of DNSSEC in IPv6 networks which parallels
+   current IPv4 practice.
+
+7.  IANA Considerations
+
+   None.
+
+Normative References
+
+   [RFC1035]  Mockapetris, P., "Domain Names - Implementation and
+              Specification", STD 13, RFC 1035, November 1987.
+
+   [RFC1886]  Thompson, S. and C. Huitema, "DNS Extensions to support IP
+              version 6", RFC 1886, December 1995.
+
+   [RFC2673]  Crawford, M., "Binary Labels in the Domain Name System",
+              RFC 2673, August 1999.
+
+   [RFC2874]  Crawford, M. and C. Huitema, "DNS Extensions to Support
+              IPv6 Address Aggregation and Renumbering", RFC 2874, July
+              2000.
+
+
+
+Bush, et. al.                Informational                      [Page 4]
+
+RFC 3363        Representation of IPv6 Addresses in DNS      August 2002
+
+
+   [RFC3152]  Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152
+              August 2001.
+
+Informative References
+
+   [RFC3364]  Austein, R., "Tradeoffs in Domain Name System (DNS)
+              Support for Internet Protocol version 6 (IPv6)", RFC 3364,
+              August 2002.
+
+Editors' Addresses
+
+   Randy Bush
+   EMail: randy@psg.com
+
+
+   Alain Durand
+   EMail: alain.durand@sun.com
+
+
+   Bob Fink
+   EMail: fink@es.net
+
+
+   Olafur Gudmundsson
+   EMail: ogud@ogud.com
+
+
+   Tony Hain
+   EMail: hain@tndh.net
+
+
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+Bush, et. al.                Informational                      [Page 5]
+
+RFC 3363        Representation of IPv6 Addresses in DNS      August 2002
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2002).  All Rights Reserved.
+
+   This document and translations of it may be copied and furnished to
+   others, and derivative works that comment on or otherwise explain it
+   or assist in its implementation may be prepared, copied, published
+   and distributed, in whole or in part, without restriction of any
+   kind, provided that the above copyright notice and this paragraph are
+   included on all such copies and derivative works.  However, this
+   document itself may not be modified in any way, such as by removing
+   the copyright notice or references to the Internet Society or other
+   Internet organizations, except as needed for the purpose of
+   developing Internet standards in which case the procedures for
+   copyrights defined in the Internet Standards process must be
+   followed, or as required to translate it into languages other than
+   English.
+
+   The limited permissions granted above are perpetual and will not be
+   revoked by the Internet Society or its successors or assigns.
+
+   This document and the information contained herein is provided on an
+   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
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+Bush, et. al.                Informational                      [Page 6]
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