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Troubleshooting
How to Troubleshoot
To end a trace in progress, enter the escape sequence (Ctrl-^ X by default). Simultaneously press and release the Ctrl,
Shift, and 6 keys and then press the X key.
Running TDR and Displaying the Results
To run TDR, enter the test cable-diagnostics tdr interface interface-id privileged EXEC command:
To display the results, enter the show cable-diagnostics tdr interface interface-id privileged EXEC command.
Enabling Debugging on a Specific Feature
Caution: Because debugging output is assigned high priority in the CPU process, it can render the system unusable.
For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions
with Cisco technical support staff. It is best to use debug commands during periods of lower network traffic and
fewer users. Debugging during these periods decreases the likelihood that increased debug command processing
overhead will affect system use.
All debug commands are entered in privileged EXEC mode, and most debug commands take no arguments. For
example, beginning in privileged EXEC mode, enter this command to enable the debugging for Switched Port Analyzer
(SPAN):
Switch# debug span-session
The switch continues to generate output until you enter the no form of the command.
If you enable a debug command and no output appears, consider these possibilities:
The switch might not be properly configured to generate the type of traffic you want to monitor. Use the show
running-config command to check its configuration.
Even if the switch is properly configured, it might not generate the type of traffic you want to monitor during the
particular period that debugging is enabled. Depending on the feature you are debugging, you can use commands
such as the TCP/IP ping command to generate network traffic.
To disable debugging of SPAN, enter this command in privileged EXEC mode:
Switch# no debug span-session
Alternately, in privileged EXEC mode, you can enter the undebug form of the command:
Switch# undebug span-session
To display the state of each debugging option, enter this command in privileged EXEC mode:
Table 73 Traceroute Text Characters
Character Description
* The probe timed out.
? Unknown packet type.
A Administratively unreachable. Usually, this output means that an access list is blocking traffic.
HHost unreachable.
N Network unreachable.
PProtocol unreachable.
Q Source quench.
UPort unreachable.
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