Network Address Translator (NAT)

A NAT device is a device that will translate one IP address into another IP address. Generally, this includes the translation of a port number into a different port number, though not necessarily.

NAT devices are useful in networks where there are limited public addresses or where there is a desire to hide the topology of an internal network from the outside world.

NAT devices break the fundemental end-to-end principle of the Internet. Even so, they are a fact of life, as virtually every enterprise network and home network relies on NAT devices in order to access services on the public Internet.

NAT devices are generally integrated with firewall devices, but the functionality of the two devices are quite different in scope and purpose.

Resources: NAT Anatomy

See Also: Firewall