11.4 Configuring and Troubleshooting PAT on the Cisco 700 Router
11.4.1 Address-translation feature

PAT, a subset of NAT, is the only address-translation feature in Cisco 700 series routers. If you wish to enable address translation on a Cisco 700 series router, you need to use PAT.

Cisco 700 series routers with Release 4.0 software support PAT, which enables local hosts on a private IP network to communicate over a public network such as the Internet. All traffic that is designated to an external address will have its source IP address and source port number translated before the packet is forwarded over the public network. IP packets returning to the private network will have their IP addresses translated back to private IP addresses.

PAT conserves network address space by enabling a single IP address to be assigned to an entire LAN. All WAN traffic is mapped to a single node-the Integrated Services Digital Network (ISDN)-side IP address of the Cisco 700 series router, as shown in the Figure.

All traffic on the public network appears to come from the Cisco 700, making the remote LAN invisible to the outside world. The advantage of using PAT on a Cisco 700 series router is that it enables hosts on private networks to communicate over public networks while conserving IP addresses.