Restrict published IPv6 addresses to ULA range

Only return AAAA/glue records within fc00::/7, filtering out public
IPv6 addresses in addition to link-local ones.

proxy.py

@@ -14,6 +14,7 @@ domain = sys.argv[1]
 port = int(sys.argv[2])
 ttl = 120
 timeout = 2
+ipv6_ula_network = ipaddress.ip_network('fc00::/7')
 
 class DynamicResolver(object):
     def __init__(self):
@@ -91,14 +92,16 @@ class DynamicResolver(object):
                 )) for addr in info.ip_addresses_by_version(IPVersion.V4Only)]
             additional += [dns.RRHeader(name=target, ttl=ttl, type=dns.AAAA, payload=dns.Record_AAAA(
                     str(addr)
-                )) for addr in info.ip_addresses_by_version(IPVersion.V6Only) if not addr.is_link_local]
+                )) for addr in info.ip_addresses_by_version(IPVersion.V6Only) if addr in ipv6_ula_network]
             return answers, [], additional
         
         def host(localname, qtype):
             if qtype == dns.AAAA:
                 mdns_type, addr_len, parse_addr = _TYPE_AAAA, 16, ipaddress.IPv6Address
+                keep_addr = lambda addr: addr in ipv6_ula_network
             else:
                 mdns_type, addr_len, parse_addr = _TYPE_A, 4, ipaddress.IPv4Address
+                keep_addr = lambda addr: not addr.is_link_local
 
             class listener(RecordUpdateListener):
                 def __init__(self):
@@ -107,7 +110,7 @@ class DynamicResolver(object):
                 def update_record(self, zc, now, record):
                     if record.type == mdns_type and len(record.address) == addr_len:
                         addr = parse_addr(record.address)
-                        if not addr.is_link_local:
+                        if keep_addr(addr):
                             self.addrs.append(str(addr))
 
             l = listener()