Open a web browser like internet explorer or Netscape. Enter the ip address of your router in the address bar of your browser. In the picture above the address bar has http://www.google.com in it. Just replace all of that with the ip address of your router. By default the ip address should be set to 192.168.1.1.
You should see a box prompting you for your username and password. Enter your username and password now. By default the username is admin, and the password is admin. Click the Ok button to log in to your router. Please visit our default username and passsword page, if the username and password shown above did not work for you.
Click the Firewall and Passwords button near the top of the page.
Click the NAT/Gaming button near the right of the page.
Click the Define Custom Service button near the center of the page.
Click the Next button near the bottom of the page.
Click the Done button near the bottom of the page.
And that is it! You are done!