Month: March 2007

I’m doing some ASP.NET development in Visual Studio 2005 at the moment, and I’ve spent the last half hour beating my head against the wall because of an obscure error message:

ASP.NET Development Server failed to start listening on port 1651.
Error message:
Only one usage of each socket address (protocol/network address/port) is normally permitted.

This happened whenever I tried to run the application, or use the ASP.NET Configuration utility. (The idea is that Visual Studio has its own webserver built in, so you don’t need to have IIS or equivalent installed on your development machine.)

I went to a command prompt and ran “netstat -a” to see whether anything else was using that port. Port 1651 wasn’t listed there, although 1652-1654 were. I ran the command again as “netstat -a -b | more” to find out ownership info, and it turned out that mIRC was using those nearby ports. So, I closed mIRC down, and was able to run the ASP.NET apps without any trouble.

Curiously, I then restarted mIRC, and I could still run the ASP.NET apps. Running netstat again, I saw that “WebDev.WebServer.EXE” was using port 1651 and “mirc.exe” was using port 2064. So, there’s probably a random element to port assignment.

Hopefully this info will be useful to other people: even if you aren’t using the same applications as me, the basic principle should still be valid (e.g. if Apache is conflicting with iTunes).