DNS64 describes a DNS server that when asked for a domain's AAAA records, but only finds A records, synthesizes the AAAA records from the A records. The first part of the synthesized IPv6 address points to a IPv6/IPv4 translator and the second part embeds the IPv4 address from the A record. The translator in question is usually a NAT64 server. The standard-track specification of DNS64 is in RFC 6147.
There are two noticeable issues with this transition mechanism:
- It only works for cases where DNS is used to find the remote host address, if IPv4 literals are used the DNS64 server will never be involved.
- Because the DNS64 server needs to return records not specified by the domain owner, DNSSEC validation against the root will fail in cases where the DNS server doing the translation is not the domain owner's server.
Read more about this topic: IPv6 Transition Mechanisms