Port forwarding on Windows computers

If you want to forward a incoming port to another computer, there’s a simple command to do this:

netsh interface portproxy add v4tov4 listenport=25 listenaddress=0.0.0.0 connectport=25 connectaddress=192.168.1.200

This command will “install” a SMTP server in one second. Nice thing is, that this port forwarding remains active even after restarting your computer.

To view all active forwards, use the following command:

netsh interface portproxy show all

To delete all active forwards or to delete one of those, use one of the following commands:

netsh interface portproxy reset
netsh interface portproxy delete v4tov4 listenport=25 listenaddress=0.0.0.0

Not so nice thing is, that you cannot use 127.0.0.1 as connectaddress. This might be necessary when you want to publish your unknown service to another port. Also UDP cannot be forwarded. To verify, that a port is actually listening or forwarding you can use netstat:

netstat -ano | findstr :25

To view what is the process name using that port (XXX is process ID):

tasklist | findstr XXX

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As an alternative you can use PassPort application http://sourceforge.net/projects/pjs-passport. It runs also on Windows XP, can forward UDP, use 127.0.0.1 as a destination and is graphical utility.