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Applying Cisco Troubleshooting Tools

Chapter Description

This sample chapter from CCNP Support Exam Certification Guide introduces some powerful troubleshooting tools that are built into the Cisco IOS. As with other tools, it is important that you identify when to use them and what information they reveal. Because some of these tools have an impact on the way routers operate and may impede the routers' utmost performance, it is essential to use them with care. To better understand the output of these commands, and to recognize what router internal operations they affect, this chapter discusses router internal components and operations. As each tool/command is introduced, its usefulness is described and tips are given on how to use it effectively.

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Foundation Topics: System Impact of Cisco Troubleshooting Tools

After completing the problem definition step, your next step (following the systematic troubleshooting process) is to start gathering detailed facts about the behavior of the devices and protocols of the production network. This task usually entails using several IOS troubleshooting tools and commands. Despite their importance in terms of the valuable information they provide, these tools inevitably utilize some processing cycles and memory of the router. Furthermore, they may disable or at least have a negative effect on some of router's internal (optimized) operations (for example, fast switching).

If you are responsible for fixing a production network's problems, you need to be familiar with troubleshooting tools. In other words, you have to know which tools you need, how to interpret each tool's output, and, very importantly, how to use each tool properly. Proper usage of a tool means that you should use it with appropriate focus and selectiveness, yet to an extent that you will gather the desired information. You must stop using these tools immediately after you attain your objective, thus you should limit the period of time during which these tools are used.

Several of the Cisco IOS show commands display information about the status of the router, its interfaces, and the rate of utilization of router resources. debug is a powerful command for finding out which packets are generated, received, and forwarded by a router. Several parameters of the debug command help focus the output on what you are interested in seeing, and hence give you a great insight on the current events and how the router handles them. But debug lowers a router's performance substantially, and that is why you need to give this command special attention.

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