Port Address Translation allows a mapping of many local private IP addresses to a single global IP address. The router maintains a table of translations by changing the source ports from the local address connection to an identifiable one on the global IP address.
To configure port address translation, configure the inside interface with
ip nat inside and the outside interface with
ip nat outside. Define an access-list for hosts and networks that will be permitted to utilise the port address translation, for example
ip access-list standard 20 then
Finally tie the configuration together with the command
ip nat inside source list <access-list> interface <outside-interface> overload