Network Address Translation (NAT)-Port Translation (PT) for Cisco software based on RFC 2766 and RFC 2765 is a migration tool that helps customers transition their IPv4 networks to IPv6 networks. Using a protocol translator between IPv6 and IPv4 allows direct communication between hosts that use different network protocols. You can use static, dynamic, port address translation, IPv4-mapped definitions for NAT-PT operation.
The figure below shows that NAT-PT runs on a device that is configured between an IPv6 network and an IPv4 network that helps connect an IPv6-only node with an IPv4-only node.
Figure 1. NAT-PT Basic Operation
NAT-PT allows direct communication between IPv6-only networks and IPv4-only networks. Dual-stack networks (networks that have IPv4 and IPv6) can have some IPv6-only hosts configured to take advantage of the IPv6 autoconfiguration, global addressing, and simpler management features, and these hosts can use NAT-PT to communicate with existing IPv4-only networks in the same organization.
One of the benefits of NAT-PT is that no changes are required to existing hosts if NAT-PT is configured, because all NAT-PT configurations are performed at the NAT-PT device. Stable IPv4 networks can introduce an IPv6 network and use NAT-PT to communicate between these networks without disrupting the network. For a seamless transition, you can use FTP between IPv4 and IPv6 hosts.
When you configure IPv6, packet fragmentation is enabled by default, to allow IPv4 and IPv6 networks to resolve fragmentation problems. Without the ability to resolve fragmentation, connectivity can be intermittent when fragmented packets are dropped or not interpreted correctly.
We do not recommend the use of NAT-PT to communicate between a dual-stack host and an IPv6-only or IPv4-only host. We do not recommend the use of NAT-PT in a scenario in which an IPv6-only network tries to communicate with another IPv6-only network via an IPv4 backbone or vice versa, because NAT-PT requires a double translation. You can use tunneling techniques for communication in these scenarios.
You can configure one the following operations for NAT-PT, but not all four.