Reverse DNS Zones
From SixXS Wiki
SIXXS offers to delegate the reverse zones for the prefix associated with a tunnel to your name server.
The standard way of doing so is to run a DNS server. However, there are also a few alternatives.
reverse.name is a wildcard DNS server. It arranges to provide a reverse DNS entry (PTR record) for every IP address in your network; for a /48 subnet, this gives 280 PTR records. Instead of storing them in a zone file, they all get automatically synthesized, leading to a DNS name which, in turn, resolves to an AAAA record for the original address. You can use this service if you want to make sure that all machines in your subnet have a reverse DNS entry, without revealing any individual machine name.