How to close TCP and UDP ports via windows command line

Question

1. open cmd

   • type in netstat -a -n -o

   • find TCP [the IP address]:[port number] .... #[target_PID]# (ditto for UDP)

   • (Btw, kill [target_PID] didn't work for me)

2. CTRL+ALT+DELETE and choose "start task manager"

   • Click on "Processes" tab

   • Enable "PID" column by going to: View > Select Columns > Check the box for PID

   • Find the PID of interest and "END PROCESS"

3. Now you can rerun the server on [the IP address]:[port number] without a problem

If you know the port that you want to free you can sort your netstat list by looking for the specif port like this:

netstat -ano | findstr :8080

Then the pid will appear at the rigth which you can kill with taskkill.

taskkill /pid 11704 /F

Also you may want to look at this question which is specifically for localhost, but I think it is relevant:

For instance you want to free the port 8080 Then, follow these commands.

 netstat -ano
 taskkill /f /im [PID of the port 8080 got from previous command]

Done!

Yes, this is possible. You don't have to be the current process owning the socket to close it. Consider for a moment that the remote machine, the network card, the network cable, and your OS can all cause the socket to close.

Consider also that Fiddler and Desktop VPN software can insert themselves into the network stack and show you all your traffic or reroute all your traffic.

So all you really need is either for Windows to provide an API that allows this directly, or for someone to have written a program that operates somewhat like a VPN or Fiddler and gives you a way to close sockets that pass through it.

There is at least one program (CurrPorts) that does exactly this and I used it today for the purpose of closing specific sockets on a process that was started before CurrPorts was started. To do this you must run it as administrator, of course.

Note that it is probably not easily possible to cause a program to not listen on a port (well, it is possible but that capability is referred to as a firewall...), but I don't think that was being asked here. I believe the question is "how do I selectively close one active connection (socket) to the port my program is listening on?". The wording of the question is a bit off because a port number for the undesired inbound client connection is given and it was referred to as "port" but it's pretty clear that it was a reference to that one socket and not the listening port.

Use TCPView: http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx
or CurrPorts: https://www.nirsoft.net/utils/cports.html

Alternatively, if you don't want to use EXTERNAL SOFTWARE (these tools don't require an installation by the way), you can simply FIRST run the netstat command (preferably netstat -b ) & then setup Local Security Policy to block the IP address of the user's machine in question, that's what I have been doing with unwanted or even unknown connections - that allows you doing everything WITHOUT ANY EXTERNAL SOFTWARE (everything comes with Windows)...