Nat Application - E-data DSL-2120 Series User Manual

outgoing packets, the ILA is the source address on the LAN, and the IGA is the source address
on the WAN. For incoming packets, the ILA is the destination address on the LAN, and the IGA
is the destination address on the WAN. NAT maps private (local) IP 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
DSL-2120/2120W keeps track of the original addresses and port numbers so incoming reply
packets can have their original values restored.
The following figure illustrates this.

5.2.1.3 NAT Application

The following figure illustrates a possible NAT application, where three inside LANs
(logical LANs using IP Alias) behind the DSL-2120/2120W can communicate with three distinct
WAN networks. More examples follow at the end of this chapter.
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Revision: V1.0
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Apr. 23, 2008