reverse_dns should also work for IPv6 prefixes != /128

[Zugschlus]

Hi,

the reverse_dns method works properly to derive the full reverse DNS name for a given IPv6 address. However, when generating zone names for IPv6 reverse zones, shorter prefixes must be used. For example, reverse_dns(2001:db8:1:2:3:4:5::/64) and reverse_dns(2001:db8:1:2::/64) should both result in
2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa and not
0.0.0.0.5.0.0.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa respective
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

The generation of the prefix should be cut once the prefix length is reached. Having a default of /128 is fine as this is by far the most common case.

If you're worried about preserving reverse_dns's backwards compatibility, please consider a new method reverse_dns_prefix or reverse_dns_delegation (although downstream software such as ansible would need to follow that).

Greetings
Marc

[jstasiak]

@Zugschlus can you link to a relevant RFC or some other kind of documentation?