11.3 Configuring NAT
11.3.3
Inside global address overloading configuration

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

  1. Configure dynamic address translation.

  2. When you define the mapping between the access list and the IP NAT pool, add the overload keyword to the ip nat inside source list access-list-number pool name overload command.

  3. Enable NAT on the appropriate interfaces by using the ip nat {inside | outside} command.

The Figure shows a sample address-overloading configuration and the corresponding topology.
Lab Activity    
  Our quickly growing company has the network number 206.222.222.0, which was assigned by ARIN. Previously the company was using dynamic address translation over an ISDN line however the company has just upgraded the line to Frame Relay. The company has been growing and has outgrown the number of valid IP addresses. The company is not able to get another class C network from ARIN, so we need to find another solution which will allow all of our employees Internet access without over running the available valid IP addresses. We have researched NAT and found that if set up properly we can translate many internal IP addresses into one valid IP address. This is called Overloading Network Address Translation. It is our job to configure the Frame Relay connection and implement the proper address translation.