IP forwarding

IP forwarding enables one workstation to sit on two LANs and to act as a gateway forwarding IP packets from one LAN to another. IP forwarding is also referred to as ?bridging? networks.

http://www.troubleshooters.com/linux/ip_fwd.htm

Port forwarding

Port forwarding allows remote computers (e.g. public machines on the Internet) to connect to a specific computer within a private LAN.

http://en.wikipedia.org/wiki/Port_forwarding

http://portforward.com/help/portforwarding.htm

PAT

Port Address Translation (PAT) is a feature of a network device that translates TCP or UDP communications made between a host and port on an outside network, and a host and port on an inside network. It allows a single IP address to be used for many internal hosts.

http://en.wikipedia.org/wiki/Port_address_translation

HTH, rate if it does

Narayan