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16
Chapter 1
Troubleshooting Methodology
The best thing to do in this situation is to make a copy of the access list
in a text editor, and then make changes that are specific to your problem.
When editing the access list, change the number of the access list. After
all of the changes are made, you can paste the access list back into the router.
Finally, go to the interface and apply the new access list. By following this
procedure, the access list is never removed from the interface.
When you create and implement action plans, it is important that you
don't fix one problem and cause another. Before implementing an action
plan, think it through or discuss it with coworkers to pick it apart, and make
sure that your solution will fix the problem without doing anything to create
adverse side effects.
Another good practice, when creating and implementing action plans, is
to change only one thing at a time, if possible. If multiple changes must be
made, it is best to make the changes in small sets. This way it is easier to
keep track of what was done, what worked, and what didn't. The observa-
tion step becomes much more effective if only a few changes are made at one
time; ideally, make only one change at a time.
To summarize, follow these practices and guidelines to create a good
action plan:
Make one change or a set of related changes at a time, and then
observe the results.
Make non-impacting changes. This means trying not to cause other
problems while implementing the changes. The more transparent the
change, the better.
Do not create security holes when changing access lists, TACACS+,
RADIUS, or other security-oriented configurations.
Most important, be able to revert to the original configuration if
unforseen problems occur as a result of the change. Always have a
backup or copy of the configuration.
Now that we have discussed creating and implementing changes, you need to
be able to monitor the network and interpret the information to verify
whether the changes implemented were effective.
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