Saturday, June 12, 2010

Yes, you do need telnet...

One of the most critical things for a router/network admin is to have a telnet client available. I know that it is old and insecure, but you can do far worse not having it in your troubleshooting tool bag (and don't get me started how big of a security risk SSH is to your network).

I do still manage devices that don't support SSH or have a crypto image on them but that is not why I missed having it. If your on a network that absolutely despises ICMP like some of the networks I've worked on before, inevitably you will be looking into a *cough* "network" problem and you need to know if the box or service is "alive". In a lot of cases you can find out simply by telneting to a port on that server that the particular service is running on. Now you still need to make sure the device you are coming from would have its traffic allowed by firewall policy along the way.

For example, you may want to know if the SSH service is open on the box you are trying to connect to:


[cfugate@lab-host ~]$ telnet www.onlinerouterlab.com 22
Trying 174.143.157.205...
Connected to www.onlinerouterlab.com.
Escape character is '^]'.
SSH-2.0-OpenSSH_5.2
^C
Connection closed by foreign host.


Now, if your running Windows Vista or Windows 7, you may have noticed you don't have the telnet client anymore. However, you can get it back simply by going to the Control Panel, Programs and look for "Turn Windows Features on or off" and check "Telnet Client" and now its back (Special thanks to LeatEDS.com)

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