Determine What Application is Using a TCP or UDP Port

Most network technicians know that running “netstat –a” at a command prompt in Windows will show you the status of application ports on the system. 

Sometimes when you install or run a new software package, you receive an error that the required port is already in use. While you can confirm with “netstat –a” that this is indeed true, what would be more useful is knowing WHAT or WHO is using the port. A lesser known netstat switch is the –b switch, which displays the executable involved in creating the connection.

“netstat –a –b” will list all listening ports, active connections and what application is bound to the port for both TCP and UDP connections. We can see for example, that port 49396 on my machine is being utilized by firefox.exe

This information can be very useful, as it provides direction on where to look if you needed to reconfigure certain applications to meet your needs.
As always, you can run the “netstat -?” to see descriptions on all the switches available and their functions.

Links of Interest