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Versions: 00 01 02 RFC 3901

Internet Engineering Task Force                     Alain Durand
INTERNET-DRAFT                             SUN Microsystems,inc.
June, 17, 2003                                       Johan Ihren
Expires December 18, 2003                             Autonomica


               DNS IPv6 transport operational guidelines
          <draft-ietf-dnsop-ipv6-transport-guidelines-00.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

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   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].

Abstract

   This memo provides guidelines and best common practice to operate DNS
   in a mixed world of IPv4 and IPv6 transport.



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.


2. Introduction to the problem of name space fragmentation:
     following the referral chain

   The caching resolver that tries to lookup 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
   a type of transport that is unavailable, 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 and the complete
   DNS hierarchy 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.

   The latter is the best situation, and a 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 they can mostly be regarded
   as "experimental". However, as soon as there is a root name server
   available over IPv6 transport it is reasonable to expect that it will
   become more common to have zones served by IPv6 servers over time.

   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.



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.  This approach could
   be revisited if/when translation techniques between IPv4 and IPv6
   were to be widely deployed.

   In order to enforce the second point, the zone validation process
   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.

   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. 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 (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   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
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   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
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   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
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