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This chapter is from the book

Exam Preparation Tasks

As mentioned in the section “How to Use This Book” in the Introduction, you have several choices for exam preparation: the exercises here; Chapter 22, “Final Preparation;” and the exam simulation questions on the CD-ROM.

Review All Key Topics

Review the most important topics in this chapter, noted with the Key Topic icon in the outer margin of the page. Table 3-5 lists a reference of these key topics and the page numbers on which each is found.


Table 3-5 Key Topics for Chapter 3

Key Topic Element


Page Number


Components in a Catalyst switch


Table 3-2

Errors in the show interfaces interface_type interface_number counters errors command



Reasons why a packet could be punted from a switch’s TCAM to its CPU



High CPU utilization troubleshooting on a switch



Identifies processes that cause excessive router CPU utilization


Table 3-3

Commands for troubleshooting high CPU utilization



Three primary modes of packet switching


Table 3-4

Commands for troubleshooting a router’s packet switching modes


Step list

Example of troubleshooting the forwarding of packets



Excessive memory utilization


Define Key Terms

Define the following key terms from this chapter and check your answers in the glossary:

  • backplane
  • control plane
  • forwarding logic
  • ingress port
  • egress port
  • half-duplex
  • full-duplex
  • TCAM
  • ARP Input process
  • Net Background process
  • IP Background process
  • TCP Timer process
  • process switching
  • fast switching
  • CEF
  • memory leak
  • memory-allocation failure
  • buffer leak

Complete Tables and Lists from Memory

Print a copy of Appendix C, “Memory Tables,” (found on the disc), or at least the section for this chapter, and complete the tables and lists from memory. Appendix D, “Memory Tables Answer Key,” also on the disc, includes completed tables and lists to check your work.

Command Reference to Check Your Memory

This section includes the most important EXEC commands covered in this chapter. It might not be necessary to memorize the complete syntax of every command, but you should be able to remember the basic keywords that are needed.

To test your memory of the commands, cover the right side of Table 3-6 with a piece of paper, read the description on the left side, and then see how much of the command you can remember.

Table 3-6 EXEC Commands


Command Syntax

A Cisco Catalyst 3750E series switch command that can be used to verify the maximum and used TCAM resources for various services and features on the switch.

show platform tcam utilization

A Cisco Catalyst switch command that can be used to display the current SDM template being used on the switch.

show sdm prefer

Displays a router’s ARP cache. (Note: If a large number of the entries are in the Incomplete state, you might suspect a malicious scan [for example, a ping sweep] of a subnet.)

show ip arp

Shows a collection of interface statistics. (Note: If the throttles, overruns, or ignored counters continually increment, you might suspect that the Net Background process is attempting to allocate buffer space for an interface from the router’s main buffer pool.)

show interface xinterface_type interface_number

Provides information about the number of TCP segments a router sends and receives, including the number of connections initiated, accepted, established, and closed. (Note: A high number of connections might explain why the TCP Timer process is consuming excessive CPU resources.)

show tcp statistics

Displays average CPU utilization over 5-second, 1-minute, and 5-minute intervals, in addition to listing all the router processes and the percentage of CPU resources consumed by each of those processes.

show processes cpu

Shows a graphical view of CPU utilization over the past 60 seconds, 1 hour, and 3 days. (Note: This graphical view can indicate whether an observed high CPU utilization is a temporary spike in utilization or whether the high CPU utilization is an ongoing condition.)

show processes cpu history

Displays multiple interface statistics, including information about the packet-switching mode of an interface.

show ip interface interface_type interface_number

Shows the contents of the fast cache for a router if fast switching is enabled.

show ip cache

Displays information about the IP Input process on a router. (Note: The CPU utilization for this process might show a high value if the CPU of a router is actively engaged in process-switching traffic.)

show processes cpu | include IP Input

Displays the router’s Layer 3 forwarding information, in addition to multicast, broadcast, and local IP addresses.

show ip cef

Verifies that a valid adjacency exists for a connected host.

show adjacency

Displays destinations reachable through the combination of the specified egress interface and next-hop IP address.

show ip cef adjacency egress_interface_id next_hop_ip_address detail

Provides information contained in a router’s adjacency table, including protocol and timer information.

show adjacency detail

Displays information about packets forwarded by the router using a packet-switching mechanism other than CEF.

show cef not-cef-switched

Shows information about memory availability on a router after the router’s Cisco IOS image has been decompressed and loaded. (Note: This command can help identify memory leaks.)

show memory allocating-process totals

Shows how many buffers (of various types) are currently free. (Note: This command can be helpful in diagnosing a buffer leak.)

show buffers

Shows how much memory is being consumed by the various BGP processes of a router.

show processes memory | include bgp

Shows the memory available on the line cards of a router.

show diag

The 300-135 TSHOOT exam focuses on practical, hands-on skills that are used by a networking professional. Therefore, you should be able to identify the commands needed to verify router and switch configurations.

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