Utilizing Cisco's Debug Commands

For a few days last week I had to travel to Sacramento for a network upgrade and installation for a customer. Pretty much everything that could go wrong did. Some days life just works that way. In the mess of having a customer's network down, I got to utilize some tools that I have only really worked with in the lab.

If you have ever typed debug ? in the Cisco CLI you have seen a plethora of available commands. If you are like me, you have hardly even scratched the surface of the possibilities. The one I found to be particularly useful was the ability to debug an interface. You can narrow down your troubleshooting quite a bit just by finding out if a particular interface is passing traffic or even attempting to communicate. If you are an IT person or network tech that deals with Cisco, I would highly recommend playing around with the debug commands the next time you are in the CLI.

A word of caution though. Some of these commands can produce a very high volume of output. If you try a debug ip packet command, you will see every ip packet the router passes. Chances are you will find it quite difficult to issue any other commands after that. If you do get in a bind, I recommend typing out the undebug all command on a text file and trying to paste it into the CLI. You will have a much better chance of getting it in there than if you try to type it in the CLI.