NAT

There are two types of network address translation. The type often popularly called simply NAT (also named Network Address Port Translation or NAPT) refers to network address translation involving the mapping of port numbers, allowing multiple machines to share a single IP address. The other, technically simpler form - also called NAT or basic NAT or static NAT - involves only address translation, not port mapping. This requires an external IP address for each simultaneous connection. Broadband routers often use this feature to allow a designated computer to accept all external connections even when the router itself uses the only available external IP address.