Internet Video Series, Part 2


Episode 14, Segment 03 of 08

The mechanisms that your router uses for intercepting, translating and relaying - SERVER - messages are generally not as automated as the mechanism for handling - CLIENT - messages. You will probably need to use your favorite web browser (as described in our movie entitled - "Managing Your Network Equipment with your Web Browser") to send - "Port Forwarding" - configuration commands to your router for every server process that you want to host on any of your local computers.

If you have a server process (such as a web server, an Internet Game server, peer-to-peer filesharing, Instant Messaging, or the well-known - "TeamSpeak" - Internet voice server) that you want to host on one of your local computers for access by clients over the Internet, it will come with documentation revealing one or more TCP or UDP ports on which it will listen for incoming requests. Some server processes need just one TCP port. Some need just one UDP port. Some need one or more of each. Some are - dynamic - and may need access to thousands of ports within some prescribed range. Some are - agile, able to adapt, (with varying efficiency), to varying port availability situations. Consult your server program's documentation as you install it on one of your local computers, and write down a list of all of the TCP and UDP ports that your server needs. You will need to teach your NAT router about those ports.

After the server software is running, fire up your favorite browser, connecting with the local IP address of your NAT router. (If your local network is typical, then this will be the same IP address that all of your PCs specify as their "default gateway". Often it is or When your router asks for your identity and password, - "log in" - using whatever information you have previously configured for router management.

After that, explore the menu choices, looking for any of the following four terms:

-- Port Triggering

-- Port Forwarding

-- DMZ (Demilitarized Zone)

-- Universal Plug and Play

All of these terms have become well-known during the past few years, and all will help you to inform your router of server processes running on your local computers.

We will examine the most complex of these terms first, and then we'll work our way back to the basics.

In each case, the information you provide will inform your router of the IP address and port numbers on which a local server process listens for incoming requests. Even though you can have as many as 253 different computers in your local network, and even though every one of those computers can have server processes running on any of 65,536 TCP Ports and 65,536 UDP ports, your router can only be told about - ONE - of your computers hosting a process that is listening on any given port.

As a consequence of this NAT limitation, even though you can host multiple servers of the same type, Internet users will only be able to use the - "well-known" - port value to communicate with - one - of them. So if you have 3 computers hosting 3 separate copies of the - "TeamSpeak" - server on the usual and customary ports, then TeamSpeak clients can use all 3 of them on your local LAN, but you can only tell your router about - one - of them, and only that one will be accesible to outsiders.

If you want outsiders to use any of the remaining TeamSpeak servers, you will have to configure your router to - "forward" - nonstandard ports to them, and you will have to inform your users of this nonstandard behavior and they will have to configure their TeamSpeak clients to use those nonstandard ports accordingly.

Episode 14, Segment 04 of 08