Add support for checking IPv6 addresses

[mlandauer]

I've just discovered an interesting situation where our IPv4 address isn't listed on any lists but our IPv6 address is.

So, it would be good to add support to this gem to be able to check IPv6 addresses.

@chrislee35 is this of interest to you? Is this something you would like to do or would you be happy to look at a PR if I was to work on the feature?

[chrislee35]

I wonder which lists support ipv6 and how they encode them ips. Sure, I'd be interested in adding support on IPv6. I'll start researching this and putting my notes here.

[chrislee35]

Looks like if I put an ipv6 address into IPAddr.new then call reverse on the address, it'll do any decompression of the ipv6 notation and reverse the octets for me. Now to do some testing.
a = "2607:f8b0:4004:805::2004"
b = IPAddr.new(a)
b.reverse.gsub('.ip6.arpa', '')
=> "4.0.0.2.0.0.0.0.0.0.0.0.0.0.0.0.5.0.8.0.4.0.0.4.0.b.8.f.7.0.6.2"

[chrislee35]

So my test client is sending well-formed queries, but without a test vector, I cannot guarantee that I would interpret the return codes correctly. Is there an RFC describing DNSBLs and test vectors?