NAT-PT, ALG, and BIA/BIS
Instead of replacing IPv4, there are several ways to coordinate the functioning
of IPv4 and v6 concurrently. NAT-protocol translation is an example of
this coexistence strategy. NAT-PT maps IPv6 addresses to IPv4 addresses. If
IPv6 is used on the inside of your network, a NAT-PT device will receive
IPv6 traffic on its inside interface and replace the IPv6 header with an IPv4
header before sending it to an outside interface. Reply traffic will be able to
follow the mapping backward to enable two-way communication.
NAT-PT is able to interpret application traffic and understand when IP information
is included in the application data.
It is also possible to connect IPv4 and IPv6 routing domains using application-
level gateways (ALG), proxies, or Bump-in-the-API (BIA) and Bumpin-
the-Stack (BIS), which are NAT-PT implementations within a host.