Troubleshootin g

The front-panel LEDs provide troubleshooting information about the switch. They show power-on self-test (POST) failures, port-connectivity problems, and overall switch performance. For a full description of the LEDs, see the "LEDs" section.

You can also get statistics from the Cluster Management Suite (CMS), the command-line interface (CLI), or a Simple Network Management Protocol (SNMP) workstation. Refer to the Catalyst 2950 Desktop Switch Software Configuration Guide, the Catalyst 2950 Desktop Switch Command Reference, or the documentation that came with your SNMP application for details.

This chapter provides these topics for troubleshooting problems:

Understanding POST results
Diagnosing problems

Understanding POST Results

While the switch powers on, it automatically begins POST, a series of tests that verifies that the switch functions properly. When the switch begins POST, the system LED is off. If POST completes successfully, the LED turns green. If POST fails, the LED turns amber.

Note POST failures are usually fatal. Call Cisco Systems if your switch does not pass POST.

Diagnosing Problems

Common switch problems fall into these categories:

Poor performance
No connectivity
Corrupted software

Table 3-1 describes how to detect and solve these problems.

Table 3-1: Common Problems and Solutions

Symptom	Possible Cause	Resolution
Poor performance or excessive errors.	Duplex autonegotiation mismatch.	Refer to the Catalyst 2950 Desktop Switch Software Configuration Guide for information about identifying autonegotiation mismatches.
	Cabling distance exceeded. Port statistics show excessive frame check sequence (FCS), late-collision, or alignment errors.	Refer to the Catalyst 2950 Desktop Switch Software Configuration Guide for information about displaying port statistics.
	For 10BASE-T, 100BASE-TX, and 1000BASE-T connections: The distance between the port and the attached device exceeds 328 feet (100 meters).	Reduce cable length to within the recommended distances.
	If the switch is attached to a repeater, the total distance between the two end stations exceeds the cabling guidelines.	Refer to your repeater documentation for cabling guidelines.
	For GBIC port connections: The distance between the GBIC port and the attached device exceeds the GBIC cabling guidelines.	Refer to your GBIC documentation for cabling guidelines.
	Bad adapter in attached device. Excessive errors found in port statistics.	Run adapter card diagnostic utility.
	Spanning Tree Protocol (STP) checking for possible loops.	Wait 30 seconds for port status LED to turn green.
No connectivity.	Incorrect or bad cable.
	No link at both ends.
	A crossover cable was used when a straight-through was required, or vice-versa.	For the correct pinouts and the proper application of crossover vs. straight-through cables, see the "Cable and Adapter Specifications" section.
	The cable is wired incorrectly.	Replace it with a tested good cable.
	STP checking for possible loops.	Wait 30 seconds for port status LED to turn green.
	Switch not recognizing a GBIC module.	Refer to your GBIC documentation for more information.
Unreadable characters on the management console.	Incorrect baud rate.	Reset the terminal-emulation software to 9600 baud.
System LED is amber, and all port LEDs are off.	Corrupted software.	Attach a monitor to the serial port to display the switch boot loader. For more information, refer to the Catalyst 2950 Desktop Switch Software Configuration Guide.
System LED is amber	Internal fan fault detected.	Check if the fan has failed by using the show env fan privileged EXEC command. If the fan has failed, call Cisco Systems.
System LED is amber	Nonfatal or fatal POST error detected.	Use the show post privileged EXEC command to see which POST test failed.

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