Network Address Translation, or NAT, is a technology that uses a router to share an Internet connection among the PCs on your private network, even though those PCs do not have a valid public IP address. There are both hardware and software NAT routers. In this particular situation, we will be configuring a Windows Server 2003 machine to act as a software based NAT router.
As you probably know, a router’s primary purpose is to regulate traffic flow between two networks, and a NAT router is no exception. The server that you will use as a NAT router must have two network interface cards (NICs) installed. One of these NICs will connect to the Internet and the other will connect to the private network. PCs on the private network will then send HTTP requests to the NAT server via the server’s private network connection. The server will then retransmit the request over the Internet on behalf of the client. When the requested Web site responds, the response is sent to the NAT server, which in turn forwards it to the client who made the original request. The client never communicates across the Internet directly.