Switch Connections
Bad or Damaged Cable
Always examine the cable for marginal damage or failure. A cable might be just good enough to connect at
the physical layer, but it could corrupt packets as a result of subtle damage to the wiring or connectors. You
can identify this situation because the port has many packet errors or the port constantly flaps (loses and
regains link).
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Examine or exchange the copper or fiber-optic cable with a known, good cable.
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Look for broken or missing pins on cable connectors.
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Rule out any bad patch panel connections or media convertors between the source and the destination.
If possible, bypass the patch panel, or eliminate faulty media convertors (fiber-optic-to-copper).
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Try the cable in another port or interface, if possible, to see if the problem follows the cable.
Ethernet and Fiber-Optic Cables
Make sure that you have the correct cable for the connection.
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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.
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For fiber-optic cables, verify that you have the correct cable for the distance and port type. Make sure
that the connected device ports both match and use the same type encoding, optical frequency, and fiber
type.
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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:
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Connect the cable from the switch to a known good device.
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Make sure that both ends of the cable are connected to the correct ports.
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Verify that both devices have power.
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Verify that you are using the correct cable type.
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Look for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect the cable
and then reconnect it.
Catalyst 3560-CX and 2960-CX Switch Hardware Installation Guide
50
Troubleshooting
Switch Connections
