Chapter 12. Troubleshooting the LAN Switching Configuration

This chapter covers the following topics:

  • Checking software versions

  • Checking hardware components

  • Understanding port errors

  • Using syslog

  • Using trace

  • Local Switched Port Analyzer

  • Remote Switched Port Analyzer

  • Cisco online resources

The primary objective of this chapter is to introduce some useful commands and techniques to help with troubleshooting a Catalyst switch. Some of the more common approaches in troubleshooting a Catalyst switch are examining the software version, checking the hardware to ensure that the device is functioning correctly and within specifications, running various commands to pinpoint the network problem, and, if all else fails, using a analyzer, such as a sniffer, to examine the packets seen on the network.

The commands provided in this chapter can help quickly rule out common issues such as bad cables and faulty ports and line modules. This chapter also addresses issues with software that might have caveats that affect the features configured on the Catalyst switch. Software features can affect the hardware configuration as well, causing the hardware to not function correctly or worst yet, reboot or crash.

This chapter examines software issues first and then progresses toward hardware problems and port errors seen on Catalyst switches. The importance of syslog and trace outputs will be discussed as well. Sometimes, it is difficult to exactly figure out what the problem is on the network because the commands provide limited functionality. In these cases, a sniffer device, which captures packets from the network, can be used to see exactly what is happening on the network.

The outline of this chapter should be used as a template when troubleshooting Catalyst switches. You should follow specific steps rather than jumping from one area to another. Examine the software and then the hardware, look for port errors, see what the syslog and trace messages say, and, finally, use a port analyzer when necessary.