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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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The Cisco IOS troubleshooting commands help you gather valuable information about the state of the network and its devices. The gathered facts help eliminate some of the possibilities, at the same time strengthening the likelihood of the hypotheses that you may have formed. Again, due to the impact that certain troubleshooting commands (debug, for example) have on some of the router's internal operations—and ultimately on the router's performance—these commands have to be used selectively, properly, and temporarily.

"Do I Know This Already?" Quiz

If you wish to evaluate your knowledge of the contents of this chapter before you get started, answer the following questions. The answers are provided in Appendix A, "Answers to Quiz Questions." If you are having difficulty providing correct answers, you should thoroughly review the entire chapter. If all or most of your answers are correct, you might want to skim this chapter for only those subjects you need to review. You can also use the "Foundation Summary" section to quickly review topics. Once you have completed the chapter, you should reevaluate yourself with the questions in the "Q&A" section at the end. Finally, use the companion CD-ROM to evaluate your knowledge of the topics and see if you need a review.

  1. Briefly explain why Cisco IOS troubleshooting commands/tools need proper handling.

  2. What does proper handling of troubleshooting tools entail?

  3. Provide a generic explanation for route caching (or fast switching) and the motivation behind it.

  4. Which of the route caching methods are not enabled by default? And from which configuration mode (prompt level) can they be enabled?

  5. With regard to speed and switching optimization, how did Cisco Systems improve the Cisco 7500 routers (in comparison to the 7000 series)?

  6. Briefly describe the advantages of Netflow switching. Also specify whether there should be any precautions with respect to enabling Netflow switching.

  7. Provide at least three examples of operations or packet types that are process switched.

  8. Before you activate Debug, what are some of its characteristics that you should consider?

  9. Before you enable debugging on a router, you are encouraged to check the router's CPU utilization. What is the command that allows you to do that? If the utilization is above 50%, are you encouraged to debug packets or to debug events?

  10. What is the default setting (for example, enabled/disabled, default destination) for message logging?

  11. What information does the output of the show logging Cisco IOS exec command display?

  12. The outputs of the show memory and the show processes [cpu] commands will most likely be asked for in which situation (loss of functionality, crash, or performance degradation)?

  13. If the output of show buffer command displays a large number of misses, increasing the value of which one of the buffer management parameters (Permanent, Min-Free, Max-Free, Initial) will most likely remedy the situation?

  14. The show processes command's output provides two numbers separated by a slash (for example, 4%/4%) for the CPU utilization over the last five seconds. How are those numbers interpreted?

  15. Which command causes the router to attempt to produce a core dump when it crashes?

2. Foundation Topics: System Impact of Cisco Troubleshooting Tools | Next Section