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.You may have to talk tonetwork administrators, other support engineers, managers, andanybody else that can provide relevant key information.Use the available testing tools and the Cisco IOS troubleshootingcommands to gather more technical and in-depth data.The most important outcome of this step is that based on its results,many possibilities or hypotheses are usually eliminated.You endup with a few possibilities surrounding a subset of your fullnetwork.Consider possibilities Use your knowledge of the network, devices, software releases,and gathered facts to formally eliminate improbable possibilitiesand set a boundary for the problem area.Order the remaining possibilities based on their likelihood.Thepossibilities should be tested and corrected according to the orderof their likelihood, in the following steps. Foundation Summary 43Table 2-1 Systematic Troubleshooting Summary (Continued)Step Actions TakenCreate action plan For each remaining possibility (arranged in order of likelihood),you must come up with one or more actions or solutions to beimplemented.It is crucial that discrete actions do not get mixed.Partition the problem area into discrete sections and plan onrepairing one section at a time (the divide and conquer method).Technical tests must be planned at this stage.Implement action plan Implement the most promising action plan.If this plan is composedof more than one action, it is important to make sure that every oneof the (individual) actions is required to be implemented at once.Otherwise, you must separate the actions and implement them oneat a time.Every action and change must be documented.If necessary, youmust be able to reverse your actions quickly.Pay attention to thesecurity and performance implications of your actions and makesure that they are acceptable.Try to stay away from invasiveactions, if possible.Observe results See if your problems/symptoms have been eliminated, but alsoinvestigate how your actions may have affected other operations.If the symptoms have disappeared and you are confident that theproblem has been solved (without creating new ones), you proceedto the next step: report the problem as solved and document theresults.If you still have unresolved issues, however, you have to gothrough another iteration of implementing actions and observingresults.Before moving to the next hypothesis, you must make an importantdecision.Do you think you should keep the actions that you justimplemented, or do you think you should reverse them? Dependingon the situation, either decision might be justifiable, regardless ofwhether you have fixed the problem.continues 44 Chapter 2: Understanding Troubleshooting MethodsTable 2-1 Systematic Troubleshooting Summary (Continued)Step Actions TakenIterate process Proceed to the next hypothesis and go about implementing itscorresponding actions.Inevitably, there will be times that you remain with no possibilityor hypothesis in hand while your network problems still exist.Ifyou cannot think of more possibilities, the reason is merely thatyou do not have all the facts.You might have overlooked certainconfigurations.You may not know some of the details about certainprotocols or devices.And lastly, you may not be aware of an IOSbug that has been reported for your IOS version/release number.Therefore, you must either gather more facts or seek help.Talk toother support engineers or consultants, use CCO s troubleshootingengine, take advantage of CCO s Open Forum or Bug Toolkit, orsimply open a case with Cisco s Technical Assistance Center(TAC).Problem solved, document When the symptoms are eliminated, document your work.This willfacts save you and others a lot of time and effort in the future.You mayalso want to document any recommendations, tips, and lessonslearned that you think might be useful to those parties involved.Accurate documentation of the date and time that you madechanges and your name and the names of those who were involvedwith this project would also be valuable information to add to yourdocumentation.Optionally, a table or index of the devices,protocols, interfaces, and so on that were somehow affected by theexperienced problem and its solution can be a useful addition toyour documentation. Q&A 45Q&AThe answers to the following questions can be found in Appendix A.Some of the questionsin this section are repeated from the Do I Know This Already Quiz so that you can gaugethe advancement of your knowledge of this subject matter.1 Write the title of each of the systematic troubleshooting method s steps in theappropriate box on the diagram below:StartFinishedYesDoproblemsymptomsstop?NoIterate process2 Explain the importance of using a systematic troubleshooting method
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