Design of a tiny multi-threaded DNS64 server

DNS64 is going to be an important service (together with NAT64) in the upcoming years of the IPv6 transition enabling the clients having only IPv6 addresses to reach the servers having only IPv4 addresses (the majority of the servers on the Internet today). This paper describes the design of MTD64, a flexible, easy to use, multi-threaded DNS64 proxy published as a free software under the GPLv2 license. All the theoretical background is introduced including the DNS message format, the operation of the DNS64+NAT64 solution and the construction of the IPv4-embedded IPv6 addresses. Our design decisions are fully disclosed from the high level ones to the details.