11.3 Configuring NAT
11.3.5 NAT to translate overlapping addresses configuration

At a minimum, IP routing and appropriate IP addresses must be configured on the router. To configure overlapping address translation, perform the following steps:

  1. Define the standard IP access list for the inside network, as discussed in the “Dynamic NAT Configuration” section.

  2. Define an IP NAT pool for the inside network by using the ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} command.

  3. Define an IP NAT pool for the outside network by using the ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} command.

  4. Define mapping between the access list and the inside global pool by using the ip nat inside source list access-list-number pool name [overload] command.

  5. Define mapping between the access list and the outside local pool by using the ip nat outside source list access-list-number pool name command.

  6. Enable NAT on the appropriate interface, as previously discussed, by using the ip nat {inside | outside} command.

Example shows a sample configuration of NAT used for translating overlapping addresses. In this example, one single router is responsible for performing the translation for inside and outside traffic. The corresponding topology is shown in Figure .
Lab Activity
  Configure an ISDN connection between Bread company router and the Butter company router, and configure it so that the two networks which have the same IP addresses can communicate together. To accomplish the communication we will configure dynamic overlapping network address translation.