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draft-ietf-dnsop-ipv6-transport-guidelines-01.txt 
Internet Engineering Task Force                         A.Durand
INTERNET-DRAFT                             SUN Microsystems,inc.
November, 24, 2003                                      J. Ihren
Expires May 25, 2004                                  Autonomica

               DNS IPv6 transport operational guidelines
          <draft-ietf-dnsop-ipv6-transport-guidelines-01.txt>

Status of this Memo

This memo provides information to the Internet community. It does not specify an Internet standard of any kind. This memo is in full conformance with all provisions of Section 10 of RFC2026

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/1id-abstracts.html

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Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

This memo provides guidelines and Best Current Practice to operate DNS in a world where queries and responses are carried in a mixed environment of IPv4 and IPv6 networks.

Acknowledgment

This document is the result of many conversations that happened in the DNS community at IETF and elsewhere since 2001. During that period of time, a number of Internet drafts have been published to clarify various aspects of the issues at stake. This document focuses on the conclusion of those discussions.

The authors would like to acknowledge the role of Pekka Savola in his thorough review of the document.

  1. Terminology

    The phrase "IPv4 name server" indicates a name server available over IPv4 transport. It does not imply anything about what DNS data is served. Likewise, "IPv6 name server" indicates a name server available over IPv6 transport. The phrase "dual-stack DNS server" indicates a DNS server that is actually configured to run both protocols, IPv4 and IPv6, and not merely a server running on a system capable of running both but actually configured to run only one.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [2119].

  2. Introduction to the Problem of Name Space Fragmentation: following the referral chain

    The caching resolver that tries to look up a name starts out at the root, and follows referrals until it is referred to a nameserver that is authoritative for the name. If somewhere down the chain of referrals it is referred to a nameserver that is only accessible over an unavailable type of transport, a traditional nameserver is unable to finish the task.

    When the Internet moves from IPv4 to a mixture of IPv4 and IPv6 it is only a matter of time until this starts to happen. The complete DNS hierarchy then starts to fragment into a graph where authoritative nameservers for certain nodes are only accessible over a certain transport. What is feared is that a node using only a particular version of IP, querying information about another node using the same version of IP can not do it because, somewhere in the chain of servers accessed during the resolution process, one or more of them will only be accessible with the other version of IP.

    With all DNS data only available over IPv4 transport everything is simple. IPv4 resolvers can use the intended mechanism of following referrals from the root and down while IPv6 resolvers have to work through a "translator", i.e. they have to use a second name server on a so-called "dual stack" host as a "forwarder" since they cannot access the DNS data directly.

    With all DNS data only available over IPv6 transport everything would be equally simple, with the exception of old legacy IPv4 name servers having to switch to a forwarding configuration.

    However, the second situation will not arise in a foreseeable time. Instead, it is expected that the transition will be from IPv4 only to a mixture of IPv4 and IPv6, with DNS data of theoretically three categories depending on whether it is available only over IPv4 transport, only over IPv6 or both.

    Having DNS data available on both transports is the best situation. The major question is how to ensure that it as quickly as possible becomes the norm. However, while it is obvious that some DNS data will only be available over v4 transport for a long time it is also obvious that it is important to avoid fragmenting the name space available to IPv4 only hosts. I.e. during transition it is not acceptable to break the name space that we presently have available for IPv4-only hosts.

  3. Policy Based Avoidance of Name Space Fragmentation

    Today there are only a few DNS "zones" on the public Internet that are available over IPv6 transport, and most of them can be regarded as "experimental". However, as soon as the root and top level domains are available over IPv6 transport, it is reasonable to expect that it will become more common to have zones served by IPv6 servers.

    Having those zones served only by IPv6-only name server would not be a good development, since this will fragment the previously unfragmented IPv4 name space and there are strong reasons to find a mechanism to avoid it.

    The RECOMMENDED approach to maintain name space continuity is to use administrative policies, as described in the next section.

  4. DNS IPv6 Transport RECOMMENDED Guidelines

    In order to preserve name space continuity, the following administrative policies are RECOMMENDED:

    • every recursive DNS server SHOULD be either IPv4-only or dual stack,
    • every single DNS zone SHOULD be served by at least one IPv4 reachable DNS server.

This rules out IPv6-only DNS servers performing full recursion and DNS zones served only by IPv6-only DNS servers. However, one could very well design a configuration where a chain of IPv6 only DNS servers forward queries to a set of dual stack DNS servers actually performing those recursive queries. This approach could be revisited if/when translation techniques between IPv4 and IPv6 were to be widely deployed.

In order to help enforcing the second point, the optional operational zone validation processes SHOULD ensure that there is at least one IPv4 address record available for the name servers of any child delegations within the zone.

5. Security Considerations

Being a critical piece of the Internet infrastructure, the DNS is a potential value target and thus should be protected. Great care should be taken not to weaken the security of DNS while introducing IPv6 operation.

Keeping the DNS name space from fragmenting is a critical thing for the availability and the operation of the Internet; this memo addresses this issue by clear and simple operational guidelines.

The RECOMMENDED guidelines are compatible with the operation of DNSSEC and do not introduce any new security issues.

6. Author Addresses

Alain Durand
SUN Microsystems, Inc
17 Network circle UMPK17-202
Menlo Park, CA, 94025
USA
Mail: Alain.Durand@sun.com

Johan Ihren
Autonomica
Bellmansgatan 30
SE-118 47 Stockholm, Sweden
Mail: johani@autonomica.se

7. Normative References

[2119] Bradner, S., "Key Words for Use in RFCs to Indicate

Requirement Levels", BCP 14, RFC 2119, March 1997.

8. Full Copyright Statement

"Copyright (C) The Internet Society (2003). 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.