Home > Forefront TMG 2010, Networking, Troubleshooting > Forefront TMG 2010 Web Proxy Auto Detect Fails

Forefront TMG 2010 Web Proxy Auto Detect Fails

May 23, 2011

Recently I received a call from a customer who was trying to resolve an issue where all web proxy clients that were configured to use Web Proxy Auto Discovery (WPAD) with DNS suddenly stopped working. We began troubleshooting by confirming that the hostname WPAD resolved to the internal IP address of the Forefront TMG firewall, which it did correctly. Next we used a telnet client to confirm that the TMG firewall was listening on TCP port 80 (used by TMG for DNS WPAD clients) and indeed it was responsive. A scan of the event logs on the firewall turned up the following warning message:

The Web Proxy filter failed to bind its socket to port 80. This may have been caused by another service that is already using the same port or by a network adapter that is not functional. To resolve this issue, restart the Microsoft Firewall service. The error code specified in the data area of the event properties indicates the cause of the failure.”

Something was listening on TCP port 80, so we opened a command prompt and entered the following command in order to determine which process was listening on this port:

netstat –ano | findstr :80

Netstat was reporting that TCP port 80 was in a listening state and bound to the IP address The process using this port was the System process (PID 4). This is unexpected, because the Forefront TMG web proxy service (wspsrv.exe) should be bound and listening on this port. Clearly this was a web service hijacking this port, so to find out more we entered the following command at a command prompt:

netsh http show servicestate

The output of this command revealed a valuable clue. Notice the registered URL below…


As it turns out, this customer had attempted to change the SQL Reporting Services Web Service URL. By assigning the Forefront TMG firewall’s internal IP address and changing the port to 80 in the Reporting Service Configuration Manager, this caused a conflict with the Forefront TMG web proxy filter, which requires TCP port 80 to provide WPAD for DNS.

To resolve the issue, the administrator chose a TCP port other than 80 and restarted the system.

  1. May 31, 2011 at 3:13 pm

    A nice piece of diagnostic work – thanks for posting it!

  2. May 31, 2011 at 3:20 pm

    My pleasure. Glad you found it helpful! 🙂

  3. Jimka
    October 19, 2012 at 12:27 pm

    Recently i was faced with this problem, i just was changed the port for WPAD in TMG.
    Thanks a lot for post.

  4. February 19, 2015 at 10:10 pm

    Thank you so much this helped !! That was the problem we had just installed SQL2012 on the server.

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