Troubleshooting guide
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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 2 Troubleshooting Overview
Troubleshooting Strategy
These steps can be grouped into a small number of troubleshooting phases:
• Make sure you have a clear, sufficient definition of the problem.
• Gather all the relevant facts and consider the likely possibilities.
• Create and implement an action plan for the most likely possibility, then observe the results.
• If the symptoms do not stop, repeat the process and try another action plan (or gather more facts).
• If the symptoms stop, make sure you document how you resolved the problem.
The following steps describe the problem-solving process outlined in Figure 2-1 in more detail:
Step 1 When analyzing a problem, draft a clear problem statement. Define the problem in terms of a set of
symptoms and the potential causes behind those symptoms.
For example, the symptom might be that the EQPT FAIL alarm has become active. Possible causes might
be physical problems, a bad interface card, or the failure of some supporting entity.
Step 2 Gather the facts you need to help isolate the symptoms and their possible causes.
Ask questions of affected users, network administrators, managers, and other key people. Collect
information from sources such as network management systems, protocol analyzer traces, output from
router diagnostic commands, or software release notes.
Step 3 Consider possible causes based on the facts you have gathered. You can also use these facts to eliminate
potential causes from your list.
For example, depending on the data, you might be able to eliminate hardware as a cause, allowing you
to focus on software. At every opportunity, try to narrow the number of potential causes so that you can
create an efficient plan of action.
Step 4 Create an action plan based on the remaining potential causes. Begin with the most likely cause, and
devise a plan in which only one variable at a time is manipulated.
This approach allows you to reproduce the solution to a specific problem. If you alter more than one
variable simultaneously, identifying the change that eliminated the symptom becomes more difficult.
Step 5 Perform each step of the action plan carefully, and test to see if the symptom disappears.
Step 6 Whenever you change a variable, gather the results. You should use the same method of gathering facts
that you used in Step 2.
Analyze the results to determine if the problem has been resolved. If it has, then the process is complete.
Step 7 If the problem has not been resolved, you must create an action plan based on the next most likely
problem in your list. Return to Step 2 (or possibly Step 1) and repeat the process until the problem is
solved.
Before trying out a new solution, make sure to undo any "fixes" you made in implementing your previous
action plan. Remember that you want to change only one variable at a time.
If you exhaust all the common causes and actions (either those outlined in this guide or those that you
have identified for your environment) and still have not resolved the problem, you should contact the
Cisco Technical Assistance Center (TAC). Refer to the preface for more information about contacting
the Cisco TAC.
This problem-solving model is just one of many such models you can use. If you are already using
another model (based on an alternative model or learned through experience), you should continue to use
it. If, in your past experience, you have not approached problems systematically and have not considered
using a problem-solving model, you should adopt a scheme such as the one outlined here.