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Chapter 3 Troubleshooting
Diagnosing Problems
•Verify that you are using the correct cable type. See Appendix A, “Connector and Cable Specifications,” for more information.
•Check for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect and then reconnect the cable.
SFP Module Port Issues
Use only Cisco small
•Bad or wrong SFP module. Exchange the suspect module with a known, good module. Verify that this module supports this platform. See the “SFP Modules” section on page
•Use the show interfaces privileged EXEC command to check the port or module
•Make sure that 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 down. 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
Use the show interfaces privileged EXEC command to check the port or interface
Ping the End Device
Check the end device by pinging it from the directly connected switch first, 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
Cisco ME 3400 Ethernet Access Switch Hardware Installation Guide
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