Wednesday, October 22, 2008

Port 80 Blocked Windows XP

Symptom: Port 80 Is Blocked On A Windows XP PC. Various browsers all produce failures appearing because http is blocked IE port 80. Alternate ports like HTTPS over 443 may work just fine. Other traffic besides port 80 may also be blocked like ICMP (ping) or SSH on port 22.

This blocking behavior is usually due to a firewall being installed and activated. First check the Windows XP firewall and disable that. Look in the control panel, Windows Firewall icon. If this firewall is disabled check for other software based firewalls installed like Zone Alarm or products from Mcafee and Symantec like Norton or other personal firewall products.

In other cases we've seen port 80 blocked on Windows XP where no firewall seems to exist. In the case i'm thinking of it was a Cisco VPN client that was the problem. The Cisco VPN client has a Zone Alarm firewall. Sometimes even after the Cisco VPN client is uninstalled port 80 is still blocked and a user cannot use a browser to http but can use https. In this case try the following solution.

Restart the Windows XP PC in Safe Mode.
Run Regedit.exe to open the registry editor.
Navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\vsdatant
Click start in the right pane and modify the value to 3.
Restart the PC and port 80 should no longer be blocked and you can use http with any browser.