Windows XP: Creating an Exception with the Windows Firewall

The Windows XP Service Pack 2 firewall has several security improvements over the Internet Connection Firewall (ICF) which originally came with the OS. Although, sometimes a firewall's rules can be too restrictive and have to be relaxed in order to let your computer do what it needs to do. Such as opening specific TCP/IP ports that allow other computers to communicate with your computer.

If you don't know what a TCP/IP port is, they're basically virtual connections on your computer that the OS or applications listen to for communication purposes. When another computer wants to talk to your computer it talks to a specific port to get the information it needs. For example, if your computer has a web service on it that runs on port 80, then when an other computer wants to access that service it will talk to port 80.

Note/Warning: Opening up ports on the Windows Firewall requires knowledge of TCP/IP. Also, if you're not careful by opening up the wrong port on your computer you can make it more vulnerable to certain types of network attacks.

To create an TCP/IP port exception to allow other computers to talk to your computer follow the instructions below:

• Open the Control Panel folder from under the Start menu, and select the Windows Firewall applet.
• Click the Exceptions tab.
• Press the "Add Port" button
• In the dialog that display, enter the name for the port that you want to open, and enter the port number(s), and finally select TCP or UDP.
• Press the OK button when done to close the dialog.
• Press the OK button when done to close the control panel

Besides blocking TCP/IP ports, the Windows firewall also blocks applications and services from talking to the Internet without your permission. For example, the 'File and Printer Sharing' service is automatically block by default. To allow other computers to access this service on your local computer, you have unblock it in the firewall.

To enable File and Printer Sharing, do the following:

• Open the Control Panel folder from under the Start menu, and select the Windows Firewall applet.
• Click the Exceptions tab.
• Find and check the 'File and Printer Sharing' checkbox.
• Press the OK button when done to close the control panel