3-2
Catalyst 2960-S Switch Hardware Installation Guide
OL-19732-04
Chapter 3 Troubleshooting
Diagnosing Problems
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).
• Examine or exchange the copper or fiber-optic cable with a known, good cable.
• Look for broken or missing pins on cable connectors.
• 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).
• Try the cable in another port or interface, if possible, to see if the problem follows the cable.
• 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 or 10/100/1000 Mb/s connections.
• 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.
• 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. See Table 2-1 for
recommended Ethernet cables.

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.
• 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 information.
• Look for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect the cable
and then reconnect it.