Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 2 Troubleshooting Overview
Troubleshooting Strategy
Step 6: Observe the Results of the Action Plan
After manipulating a variable to find a possible solution to a problem, be sure to gather results based on
the action plan. Generally, you should use the same method of gathering facts that you used in step 2 of
the methodology.
After you have analyzed the results, you must determine whether the problem has been resolved. If it
has, then this is the exit point of the iterative loop in the problem-solving model. If the problem has not
been resolved, then you must use these results to fine-tune the action plan until a solution is reached.
Step 7: Repeat the Problem-Solving Process
To reach a point where you can exit the problem/solution loop, you must make continuous progress
toward a smaller set of possibilities until you are left with only one. After narrowing the possibilities as
a result of implementing the previous action plan and observing the results, repeat the process, starting
with a new action plan based on a new list of possibilities. Continue the process until a solution is found.
Problem resolution can involve many iterations of modifications to switch configurations or gateway
configurations.
Remember that it is very important to undo any “fixes” you made that did not work. Remember that you
want to change only one variable at a time. Also, if too many changes are made at one time in the
network, it could result in a degradation of network performance and policy. This is why it is always
important to have a backout plan to undo your changes and restore the network to its previous state.
You must now implement the next step of the action plan. Check to see if your work results in a fix that
accomplishes the intended operation. Make additional changes as required. The iterations must continue
until the problem is solved. Systematically eliminate each of the possible causes until you isolate and
confirm the cause or causes so you can fix the problem.
Step 8: Resolve the Problem
If you have located the true source of the problem, then you can finish up and document the problem. If,
however, you have exhausted all common causes and actions for your environment as you attempt to
resolve a problem, then your last recourse is to contact your Cisco technical support representative. You
should have available all of the necessary information about your problem that might help the support
representative determine the possible cause of the problem.
One of the aims of this chapter is to help you develop your own processes for gathering data, resolving
problems, and preventing problems from recurring with an absolute minimum of downtime and external
intervention. Even though the recursive progression through this model may seem time-consuming, as
your troubleshooting skills mature, this process will become more automatic, and you will not need to
follow a flow diagram step-by-step.
Step 9: Document the Solution
As soon as the problem symptoms stop, chances are you have resolved the problem. At all times you
need to document your work, which involves the following:
• Maintaining a record of which steps you have already taken (for example, whether you involve
others, such as other engineers in your organization or the Cisco Technical Assistance Center.
• Providing a backout trail if it turns out that you must reverse the actions you took (for example, if
you solved the problem at hand but inadvertently caused some other problem).
• Establishing an historical record for future reference to help others learn about what occurred and
what to do about it). This record can provide a shortcut to solving a similar future problem.