Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 2 Troubleshooting Overview
Troubleshooting Tools
Commonly Used Show Commands
Some of the most commonly used Cisco IOS show commands include:
• show interfaces—displays statistics for the following network interfaces
– show interfaces ethernet
– show interfaces fddi
– show interfaces serial
• show controller t1—Displays statistics for T1 interface card controllers
• show running-config—Displays the router configuration currently running
• show startup-config—Displays the router configuration stored in nonvolatile RAM (NVRAM)
• show flash—Group of commands that display the layout and contents of Flash memory
• show buffers—Displays statistics for the buffer pools on the router
• show memory—Shows statistics about the router's memory, including free pool statistics
• show processes—Displays information about the active processes on the router
• show stacks—Displays information about the stack utilization of processes and interrupt routines,
as well as the reason for the last system reboot
• show version—Displays the configuration of the system hardware, the software version, the names
and sources of configuration files, and the boot images
For details on using and interpreting the output of show commands, refer to the relevant Cisco IOS
command references.
Debug Commands
The debug privileged EXEC commands can provide a wealth of information about the traffic being seen
(or not seen) on an interface, error messages generated by nodes on the network, protocol-specific
diagnostic packets, and other useful troubleshooting data.
Caution Be very careful when using debug commands. These commands are processor-intensive and can cause
serious network problems (degraded performance or loss of connectivity) if they are enabled on an
already heavily loaded router. When you finish using a debug command, remember to disable it with its
specific no debug command, or use the no debug all command to turn off all debugging.
Use debug commands to isolate problems, not to monitor normal network operation. Because the high
processor overhead of debug commands can disrupt switch operation, you should use them only when
you are looking for specific types of traffic or problems and have narrowed your problems to a likely
subset of causes.
Output formats vary among debug commands. Some generate a single line of output per packet, and
others generate multiple lines of output per packet. Some generate large amounts of output, and others
generate only occasional output. Some generate lines of text, and others generate information in field
format.
Note In many situations, third-party diagnostic tools can be more useful and less intrusive than the use of
debug commands. For more information, see the section Hardware Tools, page 2-15.