Cisco 3750 - Manual (Page 57)

4-3
Catalyst 3750 Metro Switch Hardware Installation Guide
OL-9160-02
Chapter 4 Troubleshooting
Diagnosing Problems
Ethernet and Fiber Cables
Make sure that you have the correct cable type for the connection:
• For Ethernet, use Category 3 copper cable for 10 Mb/s unshielded twisted pair (UTP) connections.
Use either Category 5, Category 5e, or Category 6 UTP for 10/100 or 10/100/1000 Mb/s
connections.
• For fiber-optic connectors, verify that you have the correct cable for the distance and port type.
Make sure that the ports on the connected device match and that they use the same type of encoding,
optical frequency, and fiber type. For more information about cabling, see
Appendix B, “Connector
and Cable Specifications.”
• For copper connections, determine if a crossover cable was used when a straight-through cable was
required or the reverse. Enable auto-MDIX on the switch, or replace the cable.
Link Status
Verify that both sides have link. A single broken wire or one shutdown port can cause one side to show
link, but the other side does not have link.
A link LED does not guarantee that the cable is fully functional. The cable might have encountered
physical stress that causes it to function at a marginal level. If the link light for the port does not come on:
• Connect the cable from the switch to a known, good device.
• Make sure that both ends of the cable are connected to the correct ports.
• Verify that both devices have power.
• Verify that you are using the correct cable type. See Appendix B, “Connector and Cable
Specifications.” for more information.
• Look for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect and then
reconnect the cable.
Transceiver Module Port Issues
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 incorrect SFP module. Exchange the suspect module with a known, good module. Verify that
this module supports this platform. See the
“Features” section on page 1-1 for a list of supported
SFP modules.
• Use the show interfaces privileged EXEC command to check the port or module error-disabled,
disabled, or shutdown status. Re-enable the port if necessary.
• Make sure that all you have properly cleaned and securely connected all fiber-optic connections.
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 re-enable the port.