8.6 NAT Explained

Network address translation is a critical technology, as the Internet becomes ever more widely used, with more devices becoming connected, and the availability of IP addresses is becoming a serious problem. NAT is essentially a "kluge" that deals with the issue extremely well in some situations. Longer term, the next generation of IP protocol, IPv6, is likely to be the solution this is described in "IPv6 The Next Generation Internet Protocol," earlier in this chapter. This article introduces NAT and is based upon an Accelerated Technology white paper written by Glen Johnson and Tammy Leino. (CW)

The IP Network Address Translator (NAT) protocol is a router protocol that allows nodes on a private network to transparently communicate with nodes on an external network and vice versa. Nodes on a private network have not been assigned a globally unique IP address; therefore, communication with the external network would otherwise be impossible. This transparent communication is accomplished by modifying the IP and protocol-specific headers of packets flowing to and from the private network. NAT solves three common problems with growing networks: shortage of globally unique IP addresses, firewall-like protection for the private network, and flexibility of network administration.