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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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show memory Command

The show memory exec command is often used to check the amount of a router's free memory. In troubleshooting cases where router performance is the focus, this is a major command used to see the statistics about the router's memory. Example 4-9 displays a sample output (partial) of this command executed on a Cisco 2514 router.

Example 4-9 A Sample Output of the show memory Exec Command

A_BackR#show memory

Head Total(b) Used(b) Free(b) Lowest(b) Largest(b)

Processor 90C3C 3597252 983900 2613352 2604696 2611612

I/O 400000 2097152 391980 1705172 1705172 1704752


Processor memory


Address Bytes Prev. Next Ref PrevF NextF Alloc PC What

90C3C 1064 0 91090 1 1A1630 List Elements

91090 2864 90C3C 91BEC 1 31A1630 List Headers

91BEC 2668 91090 92684 1 3150160 TTY data

92684 2000 91BEC 92E80 1 3152534 TTY Input Buf

92E80 512 92684 930AC 1 3152564 TTY Output Buf

930AC 3000 92E80 93C90 1 31B2252 Interrupt Stack




I/O memory


Address Bytes Prev. Next Ref PrevF NextF Alloc PC What

400000 260 0 400130 1 3183DD8 *Packet Data*

400130 260 400000 400260 1 3183DD8 *Packet Data*

400260 260 400130 400390 1 3183DD8 *Packet Data*

400390 260 400260 4004C0 1 3183DD8 *Packet Data*




The show memory exec command's output is organized in separate sections. In the first section you can see the summary statistics about processor memory and I/O memory (see Example 4-9). Then you can see the more detailed (block-by-block) display of memory information first for the processor memory, and then for the I/O memory. The output is not uniform across different router platforms. For example, if you execute this command on a Cisco 7000 router, the output will include processor memory and multibus memory statistics. If you execute this command on Cisco 4000 series routers, you will receive information about SRAM and I/O memory as well as processor memory. In all cases, the processor memory statistics are shown. You must pay attention to the total amount of memory, amount used, and the total amount of free memory. The Cisco TAC engineer helping you might ask questions about your router's memory utilization or simply request the output. Ask your technical support representative about the amount of free memory he/she recommends (on average) to be available.

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