NAT is an acronym for Network Address Translation. It can allow a single WAN (Wide Area Network) IP address to represent a group of LAN (Local Area Network) IP addresses. When a computer with a local IP address communicates with a server with an outside IP address, it first goes to the NAT router and writes an entire routing table. When the server responds, it sends the packets of data to the WAN IP address on the router. Once the data is received, the NAT router checks the routing table to see where the destination address is on the LAN for the data.
There are many different ways NAT routers can be configured; some include one-to-one NAT, basic NAT, overlapping, overloading, and static NAT. IP packets include the following information: source IP address, source port, destination IP address, and destination port. There are two different types of IP ports: TCP and UDP.