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This chapter contains these topics:
The LEDs on the front panel provide troubleshooting information about the switch. They show POST failures, port-connectivity problems, and overall switch performance. You can also get statistics from Device Manager, from the CLI, or from an SNMP workstation.
POST failures are usually fatal. Contact your Cisco technical support representative if your switch does not pass POST.
If you have physical access to the switch, look at the port LEDs for troubleshooting information about the switch. See the LED section for a description of the LED colors and their meanings.
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.
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.
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 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.
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:
A powered device connected to a PoE port does not receive power:
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.
Verify that there is sufficient PoE power budget to provide power to the attached device. Use the show power inline global configuration command to check on the available PoE power budget.
Verify the cable type. Many legacy powered devices, including older Cisco IP phones and access points that do not fully support IEEE 802.3af, might not support PoE when connected to the switch by a crossover cable. Replace the crossover cable with a straight-through cable.
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 privileged EXEC command to see if the interface is error-disabled, disabled, or shutdown on either side of the connection. If needed, reenable the interface.
Ping from the directly connected switch first, and then work your way back port by port, interface by interface, trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch can identify the end device MAC address in its Content-Addressable Memory (CAM) table.
If the port statistics show a large amount of alignment errors, frame check sequence (FCS), or late-collisions errors, this might mean a speed or duplex mismatch.
A common issue with speed and duplex occurs when duplex and speed settings are mismatched between two switches, between a switch and a router, or between the switch and a workstation or server. Mismatches can happen when manually setting the speed and duplex or from autonegotiation issues between the two devices.
To maximize switch performance and to ensure a link, follow one of these guidelines when changing the duplex or the speed settings.
Problems sometimes occur between the switch and third-party network interface cards (NICs). By default, the switch ports and interfaces autonegotiate. Laptops or other devices are commonly set to autonegotiate, yet sometimes autonegotiation issues occur.
To troubleshoot autonegotiation problems, try manually setting both sides of the connection. If this does not solve the problem, there could be a problem with the firmware or software on your NIC. You can resolve this by upgrading the NIC driver to the latest version.
If the port statistics show excessive FCS, late-collision, or alignment errors, verify that the cable distance from the switch to the connected device meets the recommended guidelines.
If you contact Cisco Technical Assistance, you need to know the switch serial number. You can also use the show version privileged EXEC command to see the switch serial number.
Serial number of the switch is located at the bottom of the switch. Following illustration shows all the labels at the bottom of the switch.
1 |
Compliance information |
5 |
Model number |
2 |
Country of Origin |
6 |
Serial number |
3 |
China Network Access License information |
7 |
CLEI code |
4 |
Laser label |
8 |
MAC address |