1.1.4 Configuring NAT and PAT

1.1.4 Configuring NAT and PAT

Static Translation

To configure static inside source address translation, perform the tasks in Figures and . Figure shows the use of static NAT translation. The router will translate packets from host 10.1.1.2 to a source address of 192.168.1.2.

Dynamic Translation

To configure dynamic inside source address translation, perform the tasks in Figure . The access list must permit only those addresses that are to be translated. Remember that there is an implicit “deny all” at the end of each access list. An access list that is too permissive can lead to unpredictable results. Cisco advises against configuring access lists referenced by NAT commands with the permit any command. Using permit any can result in NAT consuming too many router resources, which can cause network problems. Figure translates all source addresses passing access list 1, which have source address from 10.1.0.0/24, to an address from the pool named nat-pool1. The pool contains addresses from 179.9.8.80/24 to 179.9.8.95/24. NOTE: NAT will not translate the host 10.1.1.2, as it is not permitted for translation by the access list.

Overloading

Overloading is configured in two ways depending on how public IP addresses have been allocated. An ISP can allocate a network only one public IP address, and this is typically assigned to the outside interface which connects to the ISP. Figure shows how to configure overloading in this situation. Another way of configuring overload is if the ISP has given one or more public IP addresses for use as a NAT pool. This pool can be overloaded as shown in the configuration in Figure . Figure shows an example configuration of PAT.