Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 2 Troubleshooting Overview
Troubleshooting Tools
To minimize the negative impact of using debug commands, follow this procedure:
Step 1 Use the no logging console global configuration command on your router. This command disables all
logging to the console terminal.
Step 2 Telnet to a router port and enter the enable EXEC command.
Step 3 Use the terminal monitor command to copy debug command output and system error messages to your
current terminal display.
This permits you to view debug command output remotely, without being connected through the console
port. Following this procedure minimizes the load created by using debug commands because the
console port no longer has to generate character-by-character processor interrupts.
If you intend to keep the output of the debug command, spool the output to a file. The procedure for
setting up a debug output file, as well as complete details regarding the function and output of debug
commands is provided in Chapter 10, “Debug Command Reference,” in the Troubleshooting
Internetworking Systems manual.
Ping Command
Note It is a good idea to use the ping command when the network is functioning properly under normal
conditions so that you have something to compare against when you are troubleshooting.
To check host accessibility and network connectivity, use the ping EXEC (user) or privileged EXEC
command.
For IP, the ping command sends ICMP Echo messages. If a station receives an ICMP Echo message, it
sends an ICMP Echo Reply message back to the source. The extended command mode of the ping
command allows you to specify the supported IP header options. This allows the router to perform a
more extensive range of test options.
For detailed information on using the ping and extended ping commands, refer to the Cisco BTS 10200
Softswitch Operations Guide.
Trace Command
Note It is a good idea to use the trace command when the network is functioning properly under normal
conditions so that you have something to compare against when troubleshooting.
The trace user EXEC command discovers the routes a router's packets follow when traveling to their
destinations. The trace privileged EXEC command permits the supported IP header options to be
specified, allowing the router to perform a more extensive range of test options. The trace command uses
the error message generated by routers when a datagram exceeds its time-to-live (TTL) value. First,
probe datagrams are sent with a TTL value of 1. This causes the first router to discard the probe
datagrams and send back "time exceeded" error messages. The trace command then sends several probes
and displays the round-trip time for each. After every third probe, the TTL is increased by 1.