Networking Day 5: Port Forwarding

Today is all about port forwarding.  This is needed when you want to make a specific service available to anyone on the internet.  That service could be a game, a web server, or even Yahoo Messenger.

Ports
Anytime you connect to a server, you are connecting to a specific port. The server listens on that port for incoming connections and respond appropriately. Different port numbers are for different services.  A few examples include:

  • 80 — http
  • 21 — ftp
  • 25 — smtp (sending email)
  • 110 — pop3 (recieving email)

Before you begin the setup, you should find out what port needs to be opened.  You can figure this out by the manual or a quick internet search.

Setting up a static IP
This is necessary for most port forwarding.  Please review Day 2: Subnets for information on selecting an IP address to use.  The static IP must be in the same subnet as the dynamic IP.

Also, make sure that the DHCP on your router will not give out this IP address.  All routers will have a range of IP addresses.  If the range starts at “.100”, you can use “.99”. Also, if the range ends at “.199”, you can use “.200”.

Setting up the forwarding
Log into your router’s admin interface.  There should be “port forwarding” or “port address translation” in the menu, click this.  On this screen it should have somewhere you can enter the port and ip or a link to click to get to enter that information.  Enter the port and IP, click save, and you’re done.

Don’t forget to get your public IP address from a service like WhatIsMyIP.com.