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addresses to globally unique ones required for communication with hosts on other
networks. It replaces the original IP source address (and TCP or UDP source port
numbers for Many-to-One and Many-to-Many Overload NAT mapping) in each packet
and then forwards it to the Internet. The ROUTER keeps track of the original addresses
and port numbers so incoming reply packets can have their original values restored.
The following figure illustrates this.
NAT Application
The following figure illustrates a possible NAT application, where three inside LANs
(logical LANs using IP Alias) behind the router can communicate with three distinct
WAN networks. More examples follow at the end of this chapter.
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