How to check your port is open or not in DOS command prompt.

Do not know whether your port is open or not, use telnet command to test it.
Example, let us try to check whether local smtp port(25) is open or not.

1. Open a DOS command prompt by Start > Run > cmd
2. Type telnet 127.0.0.1 25
3. If the result shows this message:
   

   telnet 127.0.0.1 25 Connecting To 127.0.0.1...Could not open connection to the
   host, on port 25: Connect failed.
   

4. That means smtp port was not open yet.
5. If screen is change into black screen, or shows some other message which means the port was open already.

** You can use it to test on other device by changing its IP address.