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Versions: 00 01 02 03 04                                                
Internet Engineering Task Force                             Alain Durand
INTERNET-DRAFT                                           SUN Microsystem
September 6, 2001                                            Johan Ihren
Expires March 7, 2002                                      Autonomica AB

               NGtrans IPv6 DNS operational requirements and roadmap


                          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.

   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at


   This document describes IPv6 DNS operational requirements and
   deployment roadmap. It is the result of discussion from members of
   the IPv6, NGtrans, DNSops and DNSext working groups. The DNS is
   looked as a critical part of the Internet infrastructure and is used
   for much more purposes than name to address resolution.  Thus a
   smooth operation of the DNS is critical in the IPv6 transition.

   Discussion of this memo should happen in the NGtrans mailling list.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

1. IPv6 transition: Dual-stack vs IPv6 only nodes vs IPv6-mostly nodes

1.1. Incremental deployment on existing network.

   This needs to be done without disturbing IPv4 service.  This strategy
   relies heavily on dual-stack nodes and tunnels.  It is foreseen that
   this scenario is likely to happen in corporate networks.

1.2. Large scale deployment of new infrastructure

   This scenario envision large to very large networks where public IPv4
   address space is not available and private address is not practical.
   Nodes in this scenario will very likely be IPv6-only or IPv6-mostly
   (getting an IPv4 address only on demand). This scenario is likely to
   happen in the wireless/3G world. Note that those networks will still
   need to communicate with the rest of the Internet.

   Given the two above scenarios, the requirements discussed in this
   memo are not targeted at transitioning the DNS from IPv4 only to IPv6
   only, but more at the transition of IPv4 only to a mixed environment,
   where some systems will be IPv4 only, some will be IPv6 only and
   others will be dual-stacked.

2. Issues with the standard resolution process

2.1 Following the referral chain

   The caching resolver that tries to lookup an 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.

2.2 Examples of problems for an IPv6 only resolver

   This problem shows for IPv6 only resolver trying to fetch data from a
   zone that is served by IPv6 servers when somewhere in the referral
   chain, the list of name servers pointed at does not contain any IPv6
   reachable server.

   Hints for the root:

      X.ROOT-SERVERS.NET IN AAAA 3ffe:ffff:100:100::1

   In the root zone:

      org. IN NS dot-org.X.ROOT-SERVERS.NET
      dot-org.X.ROOT-SERVERS.NET IN A

   In the .org zone:

      foobar.org. IN NS ns.foobar.org
      ns.foobar.org IN A
      ns.foobar.org IN AAAA 3ffe:ffff:200:200::201

   In the foobar.org zone:

      www.foorbar.org IN AAAA 3ffe:ffff:200:200::202

   Although the zone foobar.org and the root are served by an IPv6
   server, an IPv6 only resolver can not resolve www.foobar.org because
   there is no IPv6 server for the parent zone .org.

2.3 Examples of problems for an IPv4 only resolver

   Another instance of the problem shows for an IPv4 only MTA trying to
   send mail to someone in an IPv6 only domain which has made provision
   to have an IPv4 reachable MX.

   In the .org zone:

      foobar.org. IN NS ns.foobar.org
      ns.foobar.org IN AAAA 3ffe:ffff:200:200::201

      3rd_party_dualstack_mail.org. IN NS ns.3rd_party_dualstack.org.
      ns.3rd_party_dualstack.org. IN A

   in the foobar.org zone:

      foobar.org IN MX 10 mail6.foobar.org.
      foobar.org IN MX 20 mail4.3rd_party_dualstack.org.
      mail6.foobar.org. IN AAAA 3ffe:ffff:200:200::202

   in the 3rd_party_dualstack_mail.org zone:

      mail4.3rd_party_dualstack.org. IN A

   An IPv4 only host cannot get the information about the IPv4 MX relay
   mail4.3rd_party_dualstack_mail.org because the foobar.org zone is not
   served by an IPv4 DNS server.

3. IPv4 constraints

   Due to the very large IPv4 deployment phase, any solution that will
   require any change either on the resolver binary or resolver
   configuration is out of scope.

4. IPv6 constraints

   When IPv6-only and IPv6-mostly devices send DNS queries, per
   configuration/implementation they have little choice but to use IPv6
   transport. For example, it may be too expensive, too slow or just not
   possible to get an IPv4 address for just that purpose.  With growing
   IPv6-only areas it will become increasingly cumbersome for such
   installations to maintain their DNS data only on remote systems that
   are not available over local transport.

5. Requirements

   The DNS is looked as a critical part of the Internet infrastructure
   and is used for much more purposes than name to address resolution.
   Thus, failures such as described earlier are to be prevented, and
   some kind of bridging between the two world is necessary.

   However, it should be noted that, even though bridging has to work
   both ways, it is not strictly necessary to use the same technique in
   each direction. That is, it is perfectly acceptable to build two
   different mechanisms, one to enable IPv4 only hosts to query IPv6
   only DNS servers and one for IPv6 only hosts to query IPv4 only DNS

   However, it is not clear if more than one bridging systems in a
   particular direction is a good thing or not.

5.1 IPv4 requirements

   Also, it may be the case that no bridging solution is possible to
   bridge an unmodified IPv4 resolver to an IPv6 only name server.  In
   that case, there will be a requirement that any zone be served by at
   least one IPv4 DNS server.

5.2 IPv6 requirements

   The bridging systems that enable an IPv6 resolver to query data on an
   IPv4 server will have to be in place for a long time, will be a key
   part of the IPv6 transition and will heavily be used.

   Thus, the bridging systems MUST have good scaling properties.

   The IPv6 resolver MUST have a way to discover the bridging systems.
   This discovery mechanism MUST also have good scaling properties.

   The bridging systems MUST be able to bridge any zones and, in
   particular in the absence of IPv6 name servers for the root, the
   bridging systems MUST be able to bridge the root.

6. Roadmap for DNS service in a mixed environment IPv4/IPv6

6.1 Bridging system

   A robust, scalable bridging system MUST be in place prior to large
   scale deployment IPv6 DNS deployment.

6.2 Root name service accessible via IPv6

   The first DNS query a caching resolver will send is directed to a
   root name server. This, if the configuration of the bridging system
   is derived automatically from the DNS itself, there is a strong
   requirement to make root name service available over IPv6 transport.
   If the configuration is derived any other way or is done manually,
   there is a possibility to operate the system without an IPv6
   accessible root in certain cases.  However, as this document does not
   want to preclude any particular implementation of the bridging
   systems at this point, it is highly recommended that some IPv6 enable
   root name server be in place as early as possible.  It is an
   important step to show that IPv6 DNS deployment is possible.

6.3 TLDs servers accessible via IPv6

   Having the capability to query a root name server using IPv6 is just
   the first step. The next one is to query a TLD for a NS record
   pointing to a domain name. Again, although not strictly necessary
   from a technical perspective, it is important to make sure that some
   TLD servers are accessible from the beginning via IPv6 so at least
   some label strings are resolvable with IPv6 transport without
   resorting to any fall-back mechanism.

   Also note that great care should be taken when adding IPv6 glue in
   the TLD delegation by the root.

6.4 IPv6 glue at TLD registries.

   Whenever glue is needed, it is necessary for domains delegated from a
   TLD to be able to specify an IPv6 name server address to the TLD
   registry. This is not so much a technical issue as it is a question
   of management and procedures.

6.5 Reverse path DNS servers

   Reverse DNS queries should also be supported in IPv6, for the same
   reasons as direct queries.  Today's resolvers do reverse nibbles
   queries under the ip6.int tree.  [RFC3152] has deprecated ip6.int,
   thus reverse DNS queries MUST be moved to ip6.arpa. So, as in 6.2 and
   6.3, although not strictly speaking a technical requirement, it is
   important to have at least one server for ip6.arpa accessible via

7. Security considerations

   Any bridging system, acting as open relay, could be misused to create
   denial of service attacks on external DNS servers.  Some provision
   should be made in the design of those relay to deal with this issue.

8 Editor address

   Alain Durand
   SUN Microsystems, Inc
   901 San Antonio Road
   Palo Alto, CA 94303-4900
   Mail: Alain.Durand@sun.com

   Johan Ihren
   Autonomica AB
   Bellmansgatan 30
   SE-118 47 Stockholm, Sweden

9. References

   [RFC2119] Bradner, S.,
             "Key words for use in RFCs to Indicate Requirement Levels",
             BCP 14, RFC 2119, March 199

   [RFC3152] Bush, R.,
             "Delegation of IP6.ARPA",
             RFC 3152, August 2001