Whether you're trying to troubleshoot a difficult problem, trying to clean up your network or just trying to understand some of the things you see in your routers and switches, one of the best things you can do is use a pair of Cisco tools.
First, log into your router and from the privileged exec prompt, type "show tech-support". This command, which I've mentioned previously, runs a little script that gives you just about every important show command there is, all at once. Once it's finished, save the output to a file. This can be done using Windows cut/paste from your terminal window to a text file, or if the output is too long, you can turn on logging in your terminal window and it will save the info for you. If you're using a plain Windows telnet session, you can go to properties and increase the buffers and then use the cut/paste method.
Next, browse to Cisco's Output Interpreter tool. Paste your show commands into the window, or upload your file and submit it. The tool will evaluate everything and explain everything it finds. It breaks it down for you by Errors, Warnings, Information and Helpful References.
Of course, if you've got a good idea what your problem is, you can submit just a specific show command and save yourself some time. And if you're just curious about one of the many cryptic lines on most show commands, the Output Interpreter tool is good at explaining what they mean, and referring you to more detailed information.
Note that you may need to register for a free CCO account in order to use some of the tools that the Output Interpreter will direct you to, such as the Subnet Calculator Tool.
Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.