ATL Telecom AM30 - Manual (Page 61)

ATL Telecom User Guide
AM30
6
1
Configuring Network Address Translation
This chapter provides an overview of Network Address Translation (NAT) and instructions
for modifying the default configuration on your device.
Overview of NAT
Network Address Translation is a method for disguising the private IP addresses you use on
your LAN as the public IP address you use on the Internet. You define NAT rules that specify
exactly how and when to translate between public and private IP addresses.
Definitions
A private IP address is created by a network administrator
for use only on a LAN, whereas a public IP address is
purchased from the Internet Corporation for Assigned
Names and Numbers (ICANN) for use on the Internet.
Typically, your ISP provides a public IP address for your entire
LAN, and you define the private addresses for computers on
your LAN.
In a typical NAT setup, your ISP provides you with a single public IP address to use for your
entire network. Then, you assign each computer on your LAN a unique private IP address.
(Or, you define a pool of private IP addresses for dynamic assignment to your computers, as
described in Chapter 0.) On the ROUTER you set up a NAT rule to specify that whenever
one of your computers communicates with the Internet, (that is, it sends and receives IP
data packets) its private IP address—which is referenced in each packet—will be replaced by
the LAN’s public IP address.
Definitions
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 ROUTER ).