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IP NAT Overview, Motivation, Advantages and Disadvantages
(Page 3 of 5)
Overview of IP Network Address Translation (NAT)
A very similar technique can be used
for connecting an organization's computers to the Internet. In TCP/IP
networks, this technology was first formalized in RFC 1631, The
IP Network Address Translator (NAT), adopted in May 1994. The
word “translator” refers to the device (router) that implements
NAT. More commonly, the technology as a whole is called IP Network
Address Translation (IP NAT or NAT).
 Note: The document status of RFC 1631 is “informational”. This means that technically, IP NAT is not an official Internet standard.
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A basic implementation of NAT involves
setting up an organization's internal network using one of the private
addressing ranges set aside for local IP networks.
One or more public (Internet) addresses are also assigned to the organization
as well, and one or more NAT-capable routers are installed between the
local network and the public Internet. The public IP addresses are like
“outside lines” in the telephone system, and the private addresses
are like “internal extensions”.
The NAT router plays the role of
telephone system computer and receptionist. It maps internal extensions
to outside lines as needed, and also handles "incoming calls" when required.
It does this by not just routing IP datagrams but modifying
them as needed, translating addresses in datagrams from the private
network into public addresses for transmission on the Internet, and
back again.
Over time, newer versions of NAT
have also been created that solve other problems or provide additional
capabilities. Port-Based NAT allows sharing of even more hosts
on a limited number of IP addresses, by letting two or more devices
share one IP address at a time. So-called “Twice NAT”
helps with the implementation of virtual private networks (VPN) by translating
both source and destination addresses in both incoming and outgoing
datagrams.
 Key Concept: IP Network Address Translation (IP NAT or NAT) is a technique that allows an organization to set up a network using private addresses, while still being able to communicate on the public Internet. A NAT-capable router translates private to public addresses and vice-versa as needed. This allows a small number of public IP addresses to be shared amongst a large number of devices, and provides other benefits as well (but also has some drawback).
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