IPv6 support

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Supporting IPv6 in the whitelist means two different things:
  • The DNS server that implement the whitlists reply to queries over IPv6
  • There are entries in the whitelist that refers to IPv6 addresses , and also IPv4

The first point has not too much interest, for the second one, we have the help of the RFC 5782 , where it's stated how to implement DNSBL reputation list using the reverse address format.

We have also implemented a direct format query, expanding the zeroes of the IPv6 addresses , and listing the IPv6 addresses as eight blocks of four hexdecimal digits.

As an example, the IPv6 address 2001:720:c14:200::10:227 is represented:

Zone: eswl.dnsbl.rediris.es
2001.0720.0c14.0200.0000.0000.0010.0227 IN A
2001.0720.0c14.0200.0000.0000.0010.0227 IN TXT "redirisSPF: # eeza.csic.es "
Zone: eswlrev.dnsbl.rediris.es IN A IN TXT "redirisSPF: # eeza.csic.es "

As you can see in both cases, we are maintaining the two types of register (A and TXT), that were used in the IPv4, as it's not needed to add an additional kind of register.

As a drawback, it seems that it would be more difficult to check "by hand" if an IPv6 address is listed in a DNSBL. zone.