Chapter 3 Troubleshooting
Diagnosing Problems
•Bad or incorrect XENPAK module. Replace the suspect module with a known good module. Verify that the platform supports the module. See the Table
•Use the show interfaces privileged EXEC command to check the port or module
•Make sure that all you have properly cleaned and securely connected all
Port and Interface Settings
An obvious but sometimes overlooked cause of port connectivity failure is a disabled port. Verify that the port or interface is not disabled or for some reason powered off. If a port or interface is manually shut down on one or the other side of the link, the link does not come up until you
Ping the End Device
Verify the end device connection by first pinging it from the directly connected switch, and then work your way back port by port, interface by interface, trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch can identify the end device MAC address in its
Spanning Tree Loops
Spanning Tree Protocol (STP) loops can cause serious performance issues that might appear to be port or interface problems. In this situation, the switch bandwidth is used repeatedly by the same frames, crowding out legitimate traffic.
A unidirectional link can cause loops. This occurs when the traffic that the switch sends is received by its neighbor, but the switch does not receive the traffic that is sent from the neighbor. A broken
You can enable the UniDirectional Link Detection (UDLD) protocol on the switch to help identify
Catalyst 3750 Switch Hardware Installation Guide
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