Early experience with managing IPv6-based networks in the framework of 6Bone has proven that reverse DNS in an IPv6-based environment is, in principle, at least as essential and useful as it is for the traditional IPv4-based Internet.

From a software technology perspective, no changes to the name server software in itself are required in order to support the translation of literal IPv6 addresses into name strings. For both protocol families the same basic mechanisms and the same RR type are used: the PTR record. But the rules to convert a literal address to a lookup string are different!

IPv4 uses the decimal encoded external representation of an IPv4 address to build the lookup string, e.g.

Working with

                           131.130.1.11

Leads to an attempt to find a PTR record for

11.1.130.131.in-addr.arpa.

But IPv6 uses a nibble-based hexadecimal digit encoding which generates a much longer lookup string:

2001:610:508:110:2a0:c9ff:fedd:67e7 becomes
7.e.7.6.d.d.e.f.f.f.9.c.0.a.2.0.0.1.1.0.8.0.5.0.0.1.6.0.1.0.0.2.ip6.arpa.

However, much like in the forward DNS environment, the same issues apply for the transport protocol(s). For legacy reasons IPv4 has still to be supported as the transport mechanism initially, being extended to allow IPv6 as the transport mechanism as soon as possible.

In reality, obtaining a delegation, properly configuring the name service and using the services for the IPv6 address to name translation is quite a bit more complicated:

• The strings that have to be maintained in the zone files are much longer than those for the IPv4 world (see the previous example);

• As the sTLA allocations made by the RIRs under the “bootstrap procedures” are not aligned on a nibble boundary , classless delegation mechanisms must be used to properly delegate the reverse zones;

• Initially the sub tree ipv6.int. in the DNS namespace was used to refer to the “reverse DNS for IPv6”. Alas, the “int.” TLD is reserved for organisations established under an international treaty or multi-national agreement - which is not really appropriate for reverse DNS in the IPv6 based Internet.

Efforts have already been started to move that support function back to the “arpa.” TLD - into the ip6.arpa. subtree. This migration has already begun, but it is a complex and lengthy process because the “knowledge” about the subtree in the namespace (required for the generation of the lookup label) is hardcoded into the resolver libraries.

In 2004, the migration should be finished, thus we only consider the ip6.arpa subtree.