NAT64

NAT64 is a transition mechanism that lets IPv6-only clients reach services that still only exist on IPv4. A NAT64 gateway sits at the edge of an IPv6-only network, terminates the IPv6 connection from the client, and re-originates it as an IPv4 connection toward the destination. The client never speaks IPv4 itself, and the IPv4 server never sees an IPv6 address — the translator hides each protocol from the other.

Translation uses a well-known IPv6 prefix, by default 64:ff9b::/96 (RFC 6052), to embed an IPv4 address inside an IPv6 address. A client wanting to reach 192.0.2.1 sends a packet to 64:ff9b::192.0.2.1; the NAT64 device strips the prefix, allocates a stateful mapping (similar in spirit to NAT for IPv4), and rewrites the packet. Return traffic from the IPv4 server is translated back using the same mapping, so existing IPv4 servers need no awareness of NAT64 at all.

NAT64 is normally paired with DNS64, which synthesises AAAA records for IPv4-only names by embedding the queried A record into the NAT64 prefix. An IPv6-only client doing a normal AAAA lookup for an IPv4-only host therefore gets an answer that automatically routes through the translator. The combination is what makes IPv6-only access networks practical today: most major mobile carriers run NAT64 + DNS64 so that handsets can be deployed as IPv6-only while still reaching legacy IPv4 services.

Unlike dual stack, NAT64 lets operators remove IPv4 from the access network entirely, simplifying addressing and reducing dependence on increasingly scarce public IPv4 space. It is stateful, however, so the translator must be sized and made redundant the same way any other NAT layer is.