• Remove and inspect the stack cable and stack port for bent pins or damaged connectors. If the cable is
bad, replace it with a known good cable.
Ethernet and Fiber-Optic Cables
Make sure that you have the correct cable for the connection.
• For Ethernet, use Category 3 copper cable for 10 Mb/s UTP connections. Use either Category 5, Category
5e, or Category 6 UTP for 10/100/1000 Mb/s connections.
• For fiber-optic cables, verify that you have the correct cable for distance and port type. Ensure that the
connected device ports match and use the same type of encoding, optical frequency, and fiber type.
• For copper connections, determine if a 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 link. A single broken wire or a shutdown port can cause one side to show link
even though the other side does not have link.
A port LED that is on 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 port LED does not turn on:
• Connect the cable from the switch to a known good device.
• Ensure 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.
• Check 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
A port appears to malfunction:
• Use the Mode button to show the status for all ports.
• Use the
show interfaces
privileged EXEC command to see if the port is error-disabled, disabled, or
shutdown. Reenable the port if necessary.
10/100/1000 PoE+ Port Connections
A powered device connected to a PoE port does not receive power:
• Use the Mode button to show the PoE status for all ports.
• Use the
show interfaces
privileged EXEC command to see if the port is in error-disabled, disabled, or
shutdown. Reenable the port if necessary.
• Verify that the power supply installed in the switch meets the power requirements of your connected
devices.
Catalyst 3850 Switch Hardware Installation Guide
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Troubleshooting
Ethernet and Fiber-Optic Cables
