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Jan 04

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Port Forwarding – What is it, and how can I do it?

You may have already heard about “port forwarding”. But what is it, exactly? Here is your answer: port forwarding is the redirecting of computer signals to specific electronic paths into your computer.

You need to forward a port when you are “behind” a router, which is your gateway to the World Wide Web. When network data comes from Internet to your router, the type of this data can vary a lot and ports are the way your router differentiates web sites, file downloads, and online games, because they are each assigned a port number.

By using port forwarding, the router or firewall sends the correct data to the correct place!

In a LAN (Local Area Network), every computer has an internal IP, but everyone share the same external IP (this is the one visible from outside – Internet). Let’s look at the following example.

Setting up a WebServer

So, you have your WebServer running and can access it inside your LAN (please note the standard port for HTTP communication is 80). Now you want to open it to one of your friends. The way your friend can reach your network is by your external IP. When you give your external IP to your friend and he puts it in a browser, it will send a request to your router, for port 80. But your router’s internal Firewall will probably block the access, unless you have forwarded the port.

So, by forwarding port 80 to your computer (internal IP), you will tell your router to redirect every request on port 80 to your computer.

How to Port Forward?

This is an easy question, but it doesn’t have an easy answer, as it hardly depends on the Router you have. There is a huge list of router models on this website, which will help you through the process. The site also provides a database of known application ports.

Common Used Ports

  • HTML: port 80
  • FTP: port 21
  • POP3 email: port 110
  • MSN Messenger: port 6901 and ports 6891-6900

About the author

Ricardo Dias

Ricardo Dias was born in Entroncamento, Portugal and is studying Electronic and Telecommunications Engineering at University of Aveiro. He is a researcher in robotics and is currently the Team Leader of CAMBADA@MSL team. As a hobby, he is also a freelancer Stage Lighting Designer.

Permanent link to this article: http://ricardo-dias.com/2012/01/04/port-forwarding-what-is-it-and-how-can-i-do-it/

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