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Troubleshooting
Diagnosing Problems
Ethernet and Fiber-Optic Cables
Make sure that you have the correct cable:
For Ethernet, use Category 3 copper cable for 10 Mb/s UTP connections. Use either Category 5, Category 5e, or
Category 6 UTP for 10/100, 10/100/1000 Mb/s, and PoE connections.
Verify that you have the correct fiber-optic cable for the distance and port type. Make sure that the connected device
ports match and use the same type encoding, optical frequency, and fiber type.
Determine if a copper crossover cable was used when a straight-through was required or the reverse. Enable
auto-MDIX on the switch, or replace the cable.
Link Status
Verify that both sides have a link. A broken wire or a shutdown port can cause one side to show a link even though the
other side does not have a link.
A port LED that is on does not guarantee that the cable is functional. It might have encountered physical stress, causing
it to function at a marginal level. If the port LED does not turn 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
Look for loose connections. Sometimes a cable appears to be seated but is not. Disconnect the cable, and then
reconnect it.
10/100/1000 Port Connections
If a port appears to malfunction:
Verify the status of all ports by checking the LEDs. For more information, see
Use the show interfaces privileged EXEC command to see if the port is error-disabled, disabled, or shut down.
Reenable the port if necessary.
Verify the cable type. See
SFP Module
Use only Cisco SFP modules. Each Cisco module has an internal serial EEPROM that is encoded with security information.
This encoding verifies that the module meets the requirements for the switch.
Inspect the SFP module. Exchange the suspect module with a 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. Reenable the port if needed.
Make sure that all fiber-optic connections are clean and securely connected.
Cable and Connectors, page
Cables and Adapters, page 65
Switch LEDs, page
63.
54
for information.
53.
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