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?
13 Answers
Assuming that it's a TCP (rather than UDP) port that you're trying to use:
On the server itself, use
netstat -anto check to see which ports are listening.From outside, just use
telnet host port(ortelnet host:porton 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.
If telnet is not available, download PuTTY. It is a far superior Telnet, SSH, etc. client and will be useful in many situations, not just this one, especially if you are administering a server.
Do you want a tool for doing it? There is a website at http://www.canyouseeme.org/. Otherwise, you need some other server to call you back to see if a port is open...
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