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Configuring Network Address Translation
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Definition: An IP data packet contains bits of data bundled
together in a specific format for efficient
transmission over the Internet. Such packets are
the building blocks of all Internet communication.
Each packet contains header information that
identifies the IP address of the computer that
initiates the communication (the source IP address),
the port number that the router associates with that
computer (the source port number), the IP address
of the targeted Internet computer (the destination
IP address), and other information.
When this type of NAT rule is applied, because the source IP
address is swapped out, it appears to other Internet computers
as if the data packets are actually originating from the computer
assigned your public IP address (in this case, the ADSL Barricade).
The NAT rule could further be defined to disguise the source port in
the data packet (i.e., change it to another number), so that outside
computers will not be able to determine the actual port from which
the packet originated. Data packets that arrive in response contain
the public IP address as the destination IP address and the
disguised source port number. The ADSL Barricade changes the
IP address and source port number back to the original values
(having kept track of the changes it made earlier), and then
routes the packet to the originating computer.
NAT rules such as these provide several benefits:
•
They eliminate the need for purchasing multiple public IP
addresses for computers on your LAN. You can make up your
own private IP addresses at no cost, and then have them
translated to the public IP address when your computers
access the Internet.