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Chapter 1

Troubleshooting Methodology

When the Problem Is Resolved

The problem is resolved after you implement a change, observe that the
symptoms of the problem have disappeared, and you can successfully
execute the tests that were used to aid in gathering information about
the problem.

In this example, the way to verify that the problem is solved is for Host A

to try to FTP to Host Z. If this test is successful, then the problem is resolved.

Step 8: Document the Changes

Documentation is an integral part of troubleshooting. When you keep track
of the changes that were made; which routers, switches, or hosts were
changed; and when the changes occurred, you have valuable information for
future reference. There is always the possibility that something you changed
affected something else, and you didn't notice it. If this happens, you have
documentation to refer to, so you can undo the changes. If a similar problem
occurs, you can refer to these documents to resolve the current problem,
based on what was done the last time.

Historical information is very useful in the case of a network failure. It

provides a reference for the network engineer to use to see what changes
were most recently made to the network.

The Problem-Solving Checklist

he easiest way to solve network problems is to be able to compare

current configurations against previous configurations. This sounds easy,
but it requires a lot of effort to get a system established to keep an historical
baseline of your network. A historical baseline is simply a collection of net-
work settings and configurations kept over time. This baseline makes it easy
to locate changes or differences between a current configuration and a pre-
vious one.

Baselines provide the following types of information:

Network topology

Router configurations

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