Make Peer-to-Peer File Sharing Work

My peer-to-peer (P2P) file-sharing program stopped working when I installed Service Pack 2. Is Microsoft trying to put an end to P2P, or can I fix this?

Most large companies would like to see P2P disappear, mostly because nobody has found a respectable way to make money off it. But the problem you're experiencing is almost certainly caused by the new Windows Firewall software built into SP2, which is blocking your file sharing program from establishing a connection to its server.

Note: Microsoft frequently releases updates and bug fixes for its firewall. If you decide to use the Windows Firewall, make sure you download all available updates using the Windows Update feature .

A firewall is a layer of protection that permits or denies network communication based on a predefined set of rules. These rules restrict communication so that only certain applications are permitted to use your network connection. This effectively closes back doors to your computer that viruses, hackers, and other malicious parties or applications might otherwise exploit. The Windows Firewall replaces the nearly worthless Internet Connection Firewall (ICF) found in earlier versions of Windows XP. While it's better than its predecessor, it also acts more aggressively and closes more back doors by default.


Note: If you're using a router with a built-in firewall and you don't need to protect your PC from the other computers in your local network, you can safely turn off the Windows Firewall for good .

To see if the Windows Firewall is to blame, disable it temporarily. Open the Security Center control panel, click Windows Firewall, select the "Off (not recommended)" option, and click OK.

If your P2P software now works, the firewall software is clearly the culprit. (If it still doesn't work, the problem lies elsewhere; consult your P2P software documentation for details.) Go ahead and return to the Windows Firewall window, and select the "On (recommended)" option to re-enable it. Next, choose the Exceptions tab, click the Add Program button, and find your P2P application in the list (if you don't see it, click Browse to locate the .exe file on your hard disk). Highlight the program and click OK in both boxes. The Windows firewall should now let your P2P program do its thing without interference the change will take effect immediately. (If you're using a third-party firewall program, check the software's documentation for help creating exceptions.)

If creating this exception doesn't work, return to the Exceptions tab of the Windows Firewall window and create another exception. This time, instead of basing the exception on the program filename, configure the firewall to allow all communication over the port used by your software.
Click the Add Port button, type a name for the exception (for example, P2P ), and type the port number (e.g., 6699 ). If you don't know the port number used by your P2P software, consult the software documentation. Click OK in both boxes, and give it a whirl.