I recently wrote about some 503 Service Unavailable Errors with IIS 7 that had me completely stumped. I tried everything I could think of to no avail.

Fortunately, a few of the members of the IIS 7 team stepped in to help. First, I received an email from Bill Staples, the group program manager of the IIS 7 team, kindly offered his assistance.

Meanwhile, Mike Volodarsky, a Program Manager on the IIS team in charge of the IIS 7 Web Server engine started offering help in my comments. Mike has a great blog with many useful troubleshooting tips for IIS 7. Highly recommended.

Mike brought in Chun Ye, a member of the http.sys team, who helped me get to the bottom of the problem. Here is the command he had me run.

netsh http show urlacl

The result showed that I had reserved http://+:80/ which takes precedence over all other URLs on port 80.

Reserved URL : http://+:80/
    User: METAVERSE\Phil
       Listen: Yes       Delegate: No
       SDDL:
D:(A;;GX;;;S-1-5-21-1527697538-1582451445-1978546337-1000)

The solution was to run this command:

netsh http delete urlacl url=http://+:80/

Which removed the reservation.

To be honest, I have no idea why that reservation exists. Most likely it was something dumb I did a long time ago trying to debug some other long forgotten problem. I probably forgot to revert my change or didn’t even realized I had made a change.

I don’t have a real deep understanding of http.sys reservations. What I do know about it mostly comes from this post by security guru Keith Brown.

In any case, many thanks to the IIS 7 team for your help. You rock in my book.