IPv6 Translation

Translation is a different type of solution, allowing IPv6 devices to communicate with IPv4
devices, without requiring either to be dual stack.

Stateless IP/ICMP Translation (SIIT) translates IP header fields, and NAT Protocol Translation (NAT-PT) maps IPv6 addresses to IPv4 addresses. If IPv6 is used on the inside of a network and IPv4 is used on the outside, a NAT-PT device receives IPv6 traffic on its inside interface and replaces the IPv6 header with an IPv4 header before sending it to an outside interface. Reply traffic follows the mapping backwards, enabling two-way communication.
Good NAT implementations interpret application traffic and understand when IP information is included in the application data; NAT-PT inherits this capability. For example, DNS packets
include IP addresses; therefore, NAT-PT must recognize DNS traffic and change the IPv4
addresses into IPv6 addresses, and vice-versa.
IPv4 and IPv6 routing domains can also be connected using application-level gateways (ALG) or proxies. A proxy intercepts traffic and converts between the two protocols; it can increase the transmission speed by responding to some requests using information in its cache. A separate ALG is required to support each protocol, so this method only solves specific types of translation problems.