Weekly quickTIP

Where, Oh Where Has My Little Telnet Gone?

Vista kind of hides this cool little utility that can be used for quickly peeking over a firewall or other security tricks.

• By Greg Shields
• 04/30/2007

But for those of us who like to use native tools when they're available, Telnet has some incredible uses. And I don't mean for connecting to Linux servers. You see, the version of Telnet that comes native with all versions of Windows has the capability of testing a connection on any TCP port.

Why is that useful, you ask? Have you ever found yourself stuck behind a firewall that your network administrator swears up and down has the right ports open? If you don't have a tool to check those ports, you're reliant on them to be correct. The native Windows Telnet client has always been a great tool for checking if a client can talk to a server over a particular TCP port.

If you want to find out whether a Web server is listening on TCP port 80 and you can successfully connect to that Web server through the separating firewall, type in the following:

telnet {servername} 80

If the screen immediately flashes and blanks out to a blinking cursor in the upper left of the screen, then you've successfully connected to that server on that port. If instead you get an error message without a clearing of the screen, then there's either something blocking that communication or the server isn't listening.

Remember that this is a test of two things: One, that there's an unblocked network path from client to server, and two, that the server is listening on that port.

In Windows Vista, the Telnet client isn’t as readily available as in previous versions. Like a lot of old functionality, they’ve hidden the fact that it’s there. To re-enable your old friend, navigate to Control Panel, then Programs and Features, and then click Turn Windows features on or off. Look for the Telnet Client and re-enable it.