Chapter 16: Switch Troubleshooting

In Depth

Switch troubleshooting includes both hardware and software. The switch hardware can be anything from a Supervisor Engine to a module, card, chassis, or even a power supply. The software can be the individual module software or the IOS.

In this chapter, we will focus on troubleshooting both the Command Line Interface (CLI) and the Set/Clear command−based IOS. First, I will concentrate on the physical hardware and then on the IOS troubleshooting commands. I will focus not only on the switch configuration but also on troubleshooting virtual LANs (VLANs) and the Spanning−Tree Protocol (STP).

Hardware Troubleshooting

The most common hardware problems are power supply problems, failed modules or interface problems, failed RAM, and cabling issues. Let’s first take a look at what to do in the event of a power failure, the boot−up POST, and the different indicator lights that can be used for troubleshooting.

No Power

The first indicator of a problem is the failure of a switch to power up. If there is no power to the switch, meaning the fan does not power up and no indicator lights appear lit on the front or back of the switch, follow these steps:

1.Check the physical cable for breaks or an unsecure connection.

2.Check the outlet with a multimeter for proper throughput.

3.Reseat the RAM in the chassis.

4.Check the connection and verify that all interfaces, cards, and modules are securely fastened in the chassis.

5.Make sure all gold−plated connections for the cards, modules, and RAM are not corroded and can make a good connection. To clean the gold−plated connections, I use an eraser from a pencil.

6.If necessary, contact Cisco Technical Assistance Center (TAC) or an authorized Cisco repair vendor for further troubleshooting steps and replacement parts.

Tip Heat from a failed fan followed by a cooling of components in the switch can cause a flexing of the connections. By reseating the connections, you can resolve the problem.

POST

The power on self test (POST) can be a powerful tool in solving hardware issues. On the 1900 and 2820 series switches, the POST is not displayed on the screen. Instead, as the switch powers up, all the LEDs are lit except the LED that represents the test the switch is performing. The LEDs and their related tests are shown in Table 16.1.

Table 16.1: The LEDs and the POST tests they represent.

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Tip If the light turns green, the test has been passed. The switch will not boot if all the tests are not passed, with the exception of the realtime clock test. You can enter the Diagnostic Console on a 1900/2820 series switch to activate debugging or firmware upgrade options.

Indicator Lights

Indicator lights can be your biggest signal that a hardware, software, or configuration issue exists. In addition to the Catalyst 1900/2820 series switch LED tests, which were discussed in the last section, the Supervisor Engine on the Catalyst 5000 and 6000 family has five LEDs that can indicate a problem or tell you current utilization of the switch. The Supervisor Engine LEDs indicate the system, fan, power supplies, the load utilization, and whether the Supervisor Engine is active. Figure 16.1 shows the LEDs.

Figure 16.1: The Supervisor Engine LEDs.

The switch load bar indicates the load on the switch. If the local device load is over 80 percent, then either there is a network problem such as a broadcast storm, or you need to upgrade the switching devices.

The system status lights indicate the following:

∙Red—The diagnostics on the switch have failed.

∙Orange—The PS2 power supply has failed.

∙Green—All diagnostics have passed.

The fan LED indicates the following:

∙Red—The fan has failed to power up.

∙Green—The fan is operating correctly.

The PS1 and PS2 LEDs indicate the following:

∙Red—The power supply has failed.

∙Green—The power supply is operating normally.

∙Off—The power supply bay is empty or off.

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