A DNS64 resolver with AAAA filter-like behavior (similar to the Internet Shareing on OSX El Capitan)

dns64.py

#!/usr/bin/env python2
from twisted.internet import reactor
from twisted.names import client, dns, server
import ipaddr
import socket


class SixFourResolver(client.Resolver):
    def __init__(
            self,
            resolv=None, servers=None, timeout=(1, 3, 11, 45),
            prefix="64:ff9b::"):
        client.Resolver.__init__(self, resolv, servers, timeout)

        self.prefix = prefix

    def _to_nat64_address(self, v4addr_packed):
        v4addr_str = socket.inet_ntoa(v4addr_packed)
        v6addr = ipaddr.IPv6Address(
            int(ipaddr.IPv6Address(self.prefix)) |
            int(ipaddr.IPv4Address(v4addr_str)))

        return v6addr.compressed

    def six_to_four(self, message):
        answers, authority, additional = message

        for answer in answers:
            if answer.type == dns.A:
                answer.type = dns.AAAA
                answer.payload = dns.Record_AAAA(
                    self._to_nat64_address(
                        answer.payload.address), answer.payload.ttl)

        return (answers, authority, additional)

    def lookupIPV6Address(self, name, timeout=None):
        d = self._lookup(name, dns.IN, dns.A, timeout)
        d.addCallback(self.six_to_four)

        return d


def main():
    """
    Run the server.
    """
    factory = server.DNSServerFactory(
        clients=[SixFourResolver(resolv='/etc/resolv.conf')]
    )

    protocol = dns.DNSDatagramProtocol(controller=factory)

    reactor.listenUDP(10053, protocol)
    reactor.listenTCP(10053, factory)

    reactor.run()

if __name__ == '__main__':
    raise SystemExit(main())