Catalyst 3550 Multilayer Switch Hardware Installation Guide, October 2004
Downloads: This chapterpdf (PDF - 174.0 KB) The complete bookPDF (PDF - 3.24 MB) | Feedback


Table Of Contents


Understanding POST Results

Clearing the Switch IP Address and Configuration

Diagnosing Problems


This chapter describes these troubleshooting topics:

Understanding POST Results

Clearing the Switch IP Address and Configuration

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. POST lasts approximately 1 minute. When the switch begins POST, the port LEDs turn green, the system LED blinks green, the RPS LED turns off, and then the first two port LEDs turn off. When POST completes, the port LEDs return to the status mode display, and the system LED is green. If POST fails, the system LED is amber, and the port LED associated with the test is amber.

If POST fails, the SYST LED turns amber. Table 3-1 lists causes and resolutions for a POST failure. POST failures are usually fatal. Contact your Cisco representative if your switch does not pass POST.

Note The LEDs on a Catalyst 3550-24PWR switch function differently during POST. Use the console port to view the POST results.

Clearing the Switch IP Address and Configuration

If you have configured a new switch with a wrong IP address, or if all the switch LEDs start blinking when you are trying to enter Express Setup mode, you can clear the IP address that is configured on the switch.

Note This procedure clears the IP address and all configuration information stored on the switch. Do not follow this procedure unless you want to completely reconfigure the switch.

To clear the IP address and the switch configuration information, follow these steps:

Step 1 Press and hold the Mode button.

The switch LEDs begin blinking after about 2 seconds.

Note If the switch is not configured, the LEDs are all green. You can omit Step 2 and run Express Setup to configure the switch.

Step 2 Continue holding down the Mode button. The LEDs stop blinking after 8 additional seconds, and then the switch reboots.

The switch now behaves like an unconfigured switch. You can configure the switch by using Express Setup as described in the getting started guide. You can also configure the switch by using the command-line interface (CLI) setup procedure described in "Configuring the Switch with the CLI-Based Setup Program."

Diagnosing Problems

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

You can also get statistics from the browser interface, from the CLI, or from an SNMP workstation. See the software configuration guide and the switch command reference guide on or the documentation that came with your SNMP application for details.

You can access the Cisco Technical Support website for a list of known hardware problems and extensive troubleshooting documentation:

Field notices

Security advisories

Troubleshooting resources

Factory defaults

Password recovery

Recovery from corrupted or missing software

Switch port problems

Network interface cards

Troubleshooting tools

Table 3-1 describes some common problems and their solutions.

Table 3-1 Common Problems and Solutions 


System LED is not on, and the switch does not run POST.

Check that the power cable is connected to the switch and to a known power source.

Test the power cable on another switch.

Connect a working power cable from another switch.

System LED is amber.

An internal fan fault is detected. Either check the switch itself, or use the show env user EXEC command to check for a failed fan.

The switch might be overheating. Use the show env user EXEC command to check for an overtemperature condition. If there is an overtemperature condition:

Place the switch in an environment that meets the environmental requirements given in "Technical Specifications."

Make sure that the fan intake and exhaust areas are clear.

A fatal POST error is detected. See the "Understanding POST Results" section.

No connectivity

Verify that the devices at both ends of the link are connected and powered.

Verify that the autonegotiation settings are the same at both ends.

Verify that you are using the appropriate Ethernet cable for the connected device. See Table 2-1 for cabling requirements.

Verify that the cable is good by testing it on another device. Replace it with a known working cable.

STP might be checking for possible loops. Wait 30 seconds for the port LED to turn green.

For 1000BASE-T connections, make sure to use a twisted four-pair, Category 5 cable.

The switch is not recognizing a GBIC module. See the "GBIC Module Slots" section for Cisco-recommended GBIC modules, and see your GBIC module documentation for more information.

Poor performance or excessive errors

There might be a speed and duplex autonegotiation mismatch. Use the show controllers ethernet-controller privileged EXEC command to display per-port send and receive statistics read from the hardware. You can also use the show interfaces privileged EXEC command to display the administrative and operational status of all ports or a specified port.

The cabling distance might be exceeded. Reduce the cable length to within the distances listed in the "Front-Panel Description" section.