How do I determine if a port is open on a Windows server?

Question

I'm trying to install a site under an alternative port on a server, but the port may be closed by a firewall. Is there a way to ping out or in, on a specific port, to see if it is open?

Answer 1

Assuming that it's a TCP (rather than UDP) port that you're trying to use:

1. On the server itself, use netstat -an to check to see which ports are listening.

2. From outside, just use telnet host port (or telnet host:port on Unix systems) to see if the connection is refused, accepted, or timeouts.

On that latter test, then in general:

• connection refused means that nothing is running on that port
• accepted means that something is running on that port
• timeout means that a firewall is blocking access

On Windows 7 or Windows Vista the default option 'telnet' is not recognized as an internal or external command, operable program or batch file. To solve this, just enable it: Click *Start** → Control Panel → Programs → Turn Windows Features on or off. In the list, scroll down and select Telnet Client and click OK.