network address translation (NAT)
The substitution of an official IP address for a private or unregistered IP address. NAT gives organizations more flexibility in assigning addresses internal to their network and allows users to share a limited number of registered IP addresses on an as needed basis. NAT is also used to make attacks(especially active attacks ) on the network much more difficult by avoiding the transmission of internal IP addresses over the Internet as either source or destination addresses. NAT is usually performed by a router or firewall. (See IP address, network, Internet, router, and firewall in the hard copy dictionary.)