Cisco Systems OL-16447-01 Manual De Usuario

Verify that you are using the correct cable type. See 

 for more information.

Look for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect the cable 
and then reconnect it.

Use only Cisco SFP modules on the switch. Each Cisco module has an internal serial EEPROM that is 
encoded with security information. This encoding provides a way for Cisco to identify and validate that 
the module meets the requirements for the switch. Check these items:

Bad or wrong SFP module. Exchange the suspect module with known good module. Verify that the 
module is supported on this platform. (The switch release notes on Cisco.com list the SFP modules 
that the switch supports.)

Use the show interfaces privileged EXEC command to see if the port or module is error-disabled, 
disabled, or shutdown. Re-enable the port if needed.

Make sure that all fiber connections are properly cleaned and securely connected.

An obvious but sometimes overlooked cause of port connectivity failure is a disabled interface. Verify 
that the interface is not disabled or powered off for some reason. If an interface is manually shut down 
on one side of the link or the other side, the link does not come up until you re-enable the interface. Use 
the show interfaces privileged EXEC command to see if the interface is error-disabled, disabled, or 
shutdown on either side of the connection. If needed, re-enable the interface.

Ping 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 Content-Addressable Memory (CAM) table.

STP loops can cause serious performance issues that look like port or interface problems.

Unidirectional links can cause spanning-tree loops. A unidirectional link occurs when the traffic sent by 
the switch is received by its neighbor, but does not receive traffic sent by the neighbor. A broken 
fiber-optic cable, other cabling, or a port issue could cause this one-way communication.

The UniDirectional Link Detection (UDLD) protocol helps identify unidirectional link problems. For 
more information, see the “Understanding UDLD” section in the switch software configuration guide on 
Cisco.com.