Compex Technologies NetPassage 18A - Manual (Page 88)

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To Setup Port Forwarding
Port forwarding allows the router to redirect any incoming Internet
request bearing a public IP address to a specific PC on your LAN,
based on the incoming packet’s TCP/UDP port number.
Hence, using TCP port forwarding, you can hide your web-server
behind the access point for added security, while UDP port forwarding
lets you run a secure multiplayer game server.
The following diagram shows a router with a public IP address of
203.120.90.3 and a private IP address of 192.168.168.1. Using
appropriate port forwarding settings, all incoming packets with port
number 80 will be forwarded to the web server, known on the LAN as
192.168.168.5, while those with port number 21 can be directed to the
FTP server, which has a private IP address of 192.168.168.8.