DNS on Windows Server 2003, 3rd Edition

IPv6 Forward and Reverse Mapping

Clearly, the existing A record won’t accommodate IPv6’s 128-bit addresses. RFC 1886 defines the solution: an address record that’s four times as long as an A record. That’s the AAAA (pronounced "quad A”) record. The AAAA record takes as its record-specific data the textual format of an IPv6 record as described earlier. So for example, you’d see AAAA records like this one:

ipv6-host    IN    AAAA    4321:0:1:2:3:4:567:89ab

RFC 3152 established ip6.arpa , a new reverse-mapping namespace for IPv6 addresses.^[6] Each level of subdomain under ip6.arpa represents four bits of the 128-bit address, encoded as a hexadecimal digit just like in the record-specific data of the AAAA record. The least significant (lowest order) bits appear at the far left of the domain name. Unlike the format of addresses in AAAA records, omitting leading zeros is not allowed, so there are always 32 hexadecimal digits and 32 levels of subdomain below ip6.arpa in a domain name corresponding to a full IPv6 address. The domain name that corresponds to the address in the previous example is:

b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa.

These domain names have PTR records attached, just as the domain names under in-addr.arpa do:

b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa.  IN  PTR  
mash.ip6.movie.edu.

^[6] Several aspects of IPv6 addressing have been a moving target within the Internet standards community. We should point out that ...