Network Address Translation (NAT) is a standard used to allow multiple PCs on a private network to share a single globally routable IPv4 address. NAT allows a user to have a large number of addresses internally and usually one address externally. The main reason NAT is often deployed is the scarcity of IPv4 addresses. NAT is an immediate, but temporary, solution to the problem of IPv4 address exhaustion that will eventually become unnecessary with the deployment of IPv6. The Internet Engineering Task Force has been aware of the impending exhaustion of today's address space for almost a decade. The growing use of NAT comes from a number of factors. The main factor is the global shortage of IP addresses. As