46
Troubleshooting
Diagnosing Problems
For Ethernet, use Category 3 or better copper cable for 10 Mb/s UTP connections. Use either Category 5, Category
5e, or Category 6 UTP for 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
Cable and Connectors, page 53
for information.
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
Switch LEDs, page 45
.
Use the
show interfaces
command to see if the port is error-disabled, disabled, or shut down. Reenable the port if
necessary.
Verify the cable type. See
Cable and Connectors, page 53
.
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
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.
Interface Settings
Verify that the interface is not disabled or powered off. If an interface is manually shut down on either side of the link, it
does not come up until you reenable the interface. Use the
show interfaces
command to see if the interface is
error-disabled, disabled, or shut down on either side of the connection. If needed, reenable the interface.
