How do I see if a port is in use on a windows machine?

Question

I am using Windows XP pro, and I need to know if something is registered on a port.

If so how can I tell what is on the port?

EDIT

What I mean by registered is that I am trying to test a .NET remoting application, and I need to see if the application is running or registered on a given port.

Answer 1

netstat -a -b will show all listening ports and the executable name (rather than just the PID).

If you prefer a graphical version, Microsoft's TCPView will show you the same information, updating in real-time.

Answer 2

How do you define "registered"?

Anyway, netstat -o will list the currently used and listening ports with PIDs and tasklist (or whatever process id lister is available) would sort the process name and executable out I guess? ^^

edit: Oh nice, didn't notice the netstat -b option - that's obviously the better option :)

Answer 3

Run netstat from the command line and it will show you all of the current connections. netstat -b will show you what program is using the port.

Answer 4

TCPview from the Sysinternals Suite does it in a nice, GUI way.

It includes a configurable update interval, address resolving and difference highlighting. And it is a lot faster than netstat -a -b.

Also available as a command line version (tcpvcon.exe). Both are free.