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Applying Cisco Troubleshooting Tools

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Nov 16, 2001.

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.


The answers to the following questions can be found in Appendix A. Some of the questions in this section are repeated from the "Do I Know ThisAlready" Quiz so that you can gauge the advancement of your knowledge of this subject matter.

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

2 What does proper handling of troubleshooting tools entail?

3 Define switching and specify whether it is considered a complex task.

4 Define routing and compare its complexity to switching.

5 List the sources of information used by a routing process for building its routing table.

6 When a packet is process-switched, what major tasks are performed?

7 Provide a short and generic explanation for route caching (or fast switching) and the purpose behind it.

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

9 On which component of the Cisco 7000 router is the Fast Switch Cache located?

10 Name the two major components that participate in the routing and switching tasks within a Cisco 7000 router.

11 What is the difference between the Silicon Switch Processor (SSP) and the Switch Processor (SP) with respect to the switching cache options?

12 What is the command for enabling IP fast switching on an interface?

13 What is the command for enabling IP autonomous switching on a Cisco 7000 series router interface?

14 What is the command for enabling IP silicon switching on a Cisco 7000 series router (with SSP) interface?

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

16 What switching method (route caching) can be enabled on the 7000/7500 series routers' VIP cards?

17 On which Cisco router models is Netflow switching supported? (Specify the IOS version.)

18 What information does Netflow use as the basis of identifying a flow?

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

20 What is the command for enabling IP Netflow switching on a supported router interface?

21 What are the only switching (route caching) options on the 4000, 3000, and 2500 series routers?

22 The output of which command includes information about whether fast switching is enabled/disabled for a particular protocol on a particular interface?

23 Which command can be used to see the statistics on the number of packets that are process switched and fast switched?

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

25 What are some facts about the debug privileged exec mode command that one must keep in mind before using it?

26 Which service must be loaded if you need to see a timestamp with each of the debug output lines? (Also provide the command syntax.)

27 What command enables you to see the debug output from within a Telnet session?

28 Compare debugging with the packet option to debugging with the events option.

29 Which command enables debugging for all protocols and activities? Are there any concerns regarding usage of this command?

30 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?

31 Specify the command syntax for enabling debugging for those IP packets that satisfy (are permitted by) an access list 100.

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

33 How do the logging message destination options compare in terms of the overhead they introduce to a router?

34 Which Cisco IOS router command turns console logging on and specifies the level of logging to be directed to the console?

35 By using which Cisco IOS router command can you enable sending logging messages to the internal buffer and specify the level of logging desired to be buffered?

36 Specify the Cisco IOS router command that enables sending logging messages to the virtual terminal sessions and specifies the level of logging desired to be directed to the virtual terminal lines.

37 What Cisco IOS router command would you use to make a router's logging messages be sent to a syslog server at IP address

38 What Cisco IOS router command would you use to make virtual terminal lines receive logging messages at the errors level and higher (i.e., errors, critical, alerts, emergencies)?

39 What is the severity of the following logging message?

%TR-3-WIREFAULT:Unit[0],wirefault:check the lobe cable MAU connection

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

41 What are your choices in order to make your Cisco IOS router generate Novell-compliant (ipx) pings?

42 In which situation (loss of functionality, crash, or performance degradation) will the output of the show stack command most likely be asked for?

43 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)?

44 In which situation (loss of functionality, crash, or performance degradation) will you most likely be asked to produce and provide a core dump for the technical support representative?

45 Which show command conveniently produces output equivalent to the output of show version, show running-config, show controllers, and a few other show commands?

46 Which Cisco IOS router command's output displays the current setting (value) of the config-register?

47 What is the outcome of not having an allocated and free buffer available for a packet?

48 Explain the role of the parameter called Permanent in buffer management.

49 Explain the role of the parameter called Max-Free in buffer management.

50 Explain the role of the parameter called Min-Free in buffer management.

51 Explain the role of the parameter called Initial in buffer management.

52 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?

53 What does the number of failures displayed on the output of show buffer command indicate?

54 Using what command can you find out the allocation of interface buffers on the Switch Processor of the Cisco 7x00 series routers?

55 What does the show buffers command display?

56 Which Cisco IOS command's output displays statistics about router memory (for example, amount of free processor memory)?

57 What information does the output of the Cisco IOS show processes exec command display?

58 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?

59 Specify the command (with appropriate parameters) that displays the five-seconds, one-minute, and five-minute CPU utilization for each of the active processes.

60 What information can be gathered from the output of the Cisco IOS show stacks exec command?

61 Which command allows you to generate a core dump without reloading?

62 To ensure that a core dump can be sent to a server and saved successfully, what are some of the preliminary tasks and tests you must perform?

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

64 By default, what is the name of the file that the core dump is written to?

65 Which command allows you to change the name of the core file?

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