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I have an application that I inherited that listens on port 7001 for UDP broadcasts from our in-house test equipment, and I recently updated another application that needs to do the same thing. Both applications must be able to coexist on the same computer.

Currently, when my recently updated application attempts to bind to the port to listen for UDP broadcasts and fails, it simply reports that the port is not available and suggests that the inherited application is probably running. How can I get my application to detect what application is actually listening on that port? I've done a Google search and have even searched this site, but so far I have been unable to find anything except to use Task Manager, TCPView, or netstat at the command line.

I would prefer a technique that either uses the Windows API or a Windows system COM component, since both applications are written in Visual Basic 6.0. (I know, I know, but I must maintain these applications since they are mission critical.) However, a .NET solution would would also be useful in case I need it in my new development efforts.

Peter Mortensen
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Gary Neal
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  • GetTcpTable2 can get you a process id. Similar question here [link](http://stackoverflow.com/questions/13295277/check-on-avaiable-port-using-wmi-win32-class) – user2773289 Apr 21 '14 at 19:49
  • Don't know if you can use this or not but the MSDN entry for above with some sample code is at http://msdn.microsoft.com/en-us/library/windows/desktop/bb408406(v=vs.85).aspx – Michael McGarrah Apr 21 '14 at 20:13
  • You can also get this information via WMI. Very handy thing. – user207421 Apr 21 '14 at 23:46
  • Thanks, I think the GetTcpTable2 function will get me where I need. As soon as I have time to write the code to get what I need, I will post what I've written here. – Gary Neal May 19 '14 at 15:16
  • Related: *[How do I find out which process is listening on a TCP or UDP port on Windows?](https://stackoverflow.com/questions/48198/)* – Peter Mortensen Sep 29 '22 at 19:34

1 Answers1

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Use:

netstat -n -o

That will show the process ID and from there you can either look in the Task Manager's process viewer, go to menu View → Columns... and check the Process ID (PID). Then you can see the name of the process listening on that port.

Of course, you're wanting a programmatic way of accomplishing this and the GetTCPTable2 API is best as was already suggested. In fact, if you look at the IAT (Import Address Table) for netstat.exe, it actually uses that API to get that information.

There is a way to communicate directly with a command window and get its output using pipes and it would work fine, but the ideal way is to simply use the same API netstat uses.

Peter Mortensen
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Daniel W. Elkins
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  • Thanks, this should get me where I needed. I haven't had time to go further with this but as soon as I have some working code I will post it here. – Gary Neal May 19 '14 at 15:16
  • Only `netstat --all --program | grep 8090` worked for me. Just sharing. net-tools 1.60 netstat 1.42 (2001-04-15) – Felipe Alvarez Dec 31 '14 at 03:36