Chapter 16: Switch Troubleshooting; In Depth; Hardware Troubleshooting; No Power - Cisco RJ-45-to-AUX Brochure

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.
Warning The following steps are my recommendation, based on troubleshooting procedures I use
every day. These steps do not come from Cisco documentation.

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.
Warning
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.
Make sure you use proper grounding techniques before removing or touching any
components, and that the switch is unplugged from all power sources.
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