DNSEXT Working Group Randy Bush (ed.) Alain Durand (ed.) Bob Fink (ed.) Olafur Gudmundsson (ed.) Tony Hain (ed.)
<draft-ietf-dnsext-ipv6-addresses-00.txt><draft-ietf-dnsext-ipv6-addresses-01.txt> Updates: RFC 1886, RFC 2673, RFC 2874 Representing IPv6 addresses in DNS. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Comments should be sent to the authors or the DNSEXT WG mailing list email@example.com This draft expires on March 25,September 1, 2002. Copyright Notice Copyright (C) The Internet Society (2001).(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 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. The main arguments and the issues are covered in a separate document[Tradeoff] 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. 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 recommend 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, since we do not ever expect to see delegation in the least significant possible hexadecimal label. That is, we do not ever expect to see an IPv6 address architecture that advocates address delegation in the least significant four bits of an IPv6 address.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. 4 DNAME in IPv6 reverse tree The issues for DNAME chaining in the reverse tree are substantially identical to the issues for A6 chaining in the forward tree. 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 ,Elz, Johan Ihren ,Ihren, Edward Lewis, Bill ManningManning, 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. References: [RFC1035] P. Mockapetris, ``Domain Names - Implementation and Specification'' STD 13, RFC 1035, November 1987. [RFC1886] S. Thompson, C. Huitema, ``DNS Extensions to support IP version 6'', RFC 1886, December 1995. [RFC2673] M. Crawford ``Binary Labels in the Domain Name System``, RFC 2673, August 1999. [RFC2874] M. Crawford, C. Huitema, ``DNS Extensions to Support IPv6 Address Aggregation and Renumbering'', RFC 2874, July 2000. [RFC3152] R. Bush, ``Delegation of IP6.ARPA'', RFC 3152 also BCP0049, August 2001, [Tradeoff] R. Austein, ``Tradeoffs in DNS support for IPv6'', Work in progress, draft-ietf-dnsext-ipv6-dns-tradeoffs-xx.txt, July 2001. Editors Address Randy Bush <firstname.lastname@example.org> Alain Durand <email@example.com> Bob Fink <firstname.lastname@example.org> Olafur Gudmundsson <email@example.com> Tony Hain <firstname.lastname@example.org> Full Copyright Statement Copyright (C) The Internet Society (2001).(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. 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