If one really wants IPv4 to IPv6 it would be easy enough to do a TCP service which is registered in the DNS and is reachable over IPv4 that takes a IPv6 address, transport and port tuple and returns a IPv4 address and port that the client can connect to using IPv4 over the specified transport. Such a service would be offered as part of a NAT64, MAP-T, MAP-E, DS-Lite and would establish a time limited inbound mapping to the requested end point from the IPv4 source address of the service request. The hard part of IPv4 to IPv6 is establishing the mapping. This would do so with a extra step performed by the IPv4 client. example.com. AAAA 2001:0db8:85a3:0000:0000:8a2e:0370:7334 _4to6._tcp.example.com SRV 0 0 <TBD> nat64.example.net. nat64.example.net. A 128.66.0.1 It may also pay to also return a session nonce which is added as a IPv4 option. Need to think about this some more. This is similar in concept to previous work where a A record is added to the DNS on demand but the returned address is limited to a single client. Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: marka@xxxxxxx