This chapter describes these switch module troubleshooting topics:
•Resetting the Switch Module
•How to Replace a Failed Stack Member
The LEDs on the front panel provide troubleshooting information about the switch module. They show POST failures, port-connectivity problems, and fault indications. You can also get information from the device manager, from the CLI, or from an SNMP workstation. See the switch module software configuration guide and the command reference guide on Cisco.com or the documentation that came with your SNMP application for details.
Verify Switch Module POST Results
As the switch module powers on, it begins the power-on self-test (POST), a series of tests that runs automatically to ensure that the switch module functions properly. It might take several minutes for the switch module to complete POST. When POST completes successfully, the System LED remains green. The other LEDs turn off and return to their operating status. If the switch module fails POST, the System LED is amber.
Note POST failures are usually fatal. Contact your Cisco technical support representative if your switch module does not pass POST.
Verify Switch Module LEDs
If you have physical access to the switch module, look at the port LEDs for troubleshooting information about the switch module. See the "Switch Module LEDs" section on page 1-5 for a description of the LED colors and their meanings.
Verify Switch Module Connections
Review this section when troubleshooting switch module connection problems.
Bad or Damaged Cable
Always evaluate 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). You should:
•Inspect 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 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.
•StackWise Plus cable: remove and inspect the cable and StackWise Plus port for bent pins or damaged connectors. If the StackWise Plus cable is bad, replace it with a known good cable.
Ethernet and Fiber Cables
Make sure that you have the correct cable type for the connection:
•For Ethernet, use Category 3 copper cable for 10 Mb/s UTP connections. Use Category 5, Category 5e, or Category 6 UTP for 10/100 or 10/100/1000 Mb/s connections.
•For fiber-optic connectors, 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 more information about cabling, see the "10-Gigabit Ethernet X2 Transceiver Module Cable Specifications" section on page B-3.
•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 module, or replace the cable. See Table 2-1 for recommended Ethernet cables.
Verify that both sides have link. A single broken wire or one shutdown port can cause one side to show link, but the other side does not have link.
A link LED 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 link light for the port does not come on:
•Connect the cable from the switch module 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 more information.
•Look for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect the cable, and then reconnect it.
Use only Cisco X2 transceiver modules on the switch module. Each Cisco module has an internal serial EEPROM that is encoded with security information. This encoding provides a way for Cisco to identify and validate that the module meets the requirements for the switch module. Evaluate these items:
•Bad or wrong X2 transceiver module. Exchange suspect module with known good module. Verify that the module is supported on this platform. (The switch module release notes on Cisco.com list the X2 modules that the switch module supports.)
•Use the show interfaces privileged EXEC command to verify the port or module error-disabled, disabled, or shutdown status. Re-enable the port if needed.
•Make sure that all fiber connections are properly cleaned and securely connected.
•For CX4 module connections, make sure that cable routing does not violate the minimum allowed cable-bend radius. See the module documentation for specific cabling requirements.
•For LX4 modules, we recommend a mode conditioning patch for MMF applications.
Port and Interface Settings
An obvious but sometimes overlooked cause of port connectivity failure is a disabled port. Verify that the port or interface is not disabled or powered down for some reason. If a port or interface is manually shut down on one side of the link or the other side, the link does not come up until you re-enable the port. Use the show interfaces privileged EXEC command to verify the port or interface error-disabled, disabled, or shutdown status on both sides of the connection. If needed, re-enable the port or the interface.
Ping End Device
Test the end device by pinging from the directly connected switch module 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 module can see the end device MAC address in its Content-Addressable Memory (CAM) table.
Spanning Tree Loops
Spanning Tree Protocol (STP) loops can cause serious performance issues that look like port or interface problems. In this situation, the switch module bandwidth is used over and over again by the same frames, leaving little room for legitimate traffic.
Loops can be caused by a unidirectional link. A unidirectional link occurs whenever the traffic sent by the switch module is received by its neighbor, but the traffic from the neighbor is not received by the switch module. A broken fiber-optic cable, other cabling, or a port issue could cause this one-way communication.
You can enable UniDirectional Link Detection (UDLD) on the switch module to help identify difficult-to-find unidirectional link problems. UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD detects unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links due to one-way traffic on fiber-optic and twisted-pair links and due to misconnected interfaces on fiber-optic links. For information about enabling UDLD on the switch module, see the "Understanding UDLD" section in the software configuration guide for this release.
Verify Switch Module Performance
Review this section when troubleshooting switch module performance problems.
Speed, Duplex, and Autonegotiation
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 is when the duplex settings are mismatched between two switch modules, between a switch module and a router, or between the switch module and a workstation or server. This can happen when manually setting the speed and duplex or from autonegotiation issues between the two devices. A mismatch occurs under these circumstances:
•A manually set speed or duplex parameter is different from the manually set speed or duplex parameter on the connected port.
•A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.
To maximize switch module performance and ensure a link, follow one of these guidelines when changing the settings for duplex and speed:
•Let both ports autonegotiate both speed and duplex.
•Manually set the speed and duplex parameters for the ports on both ends of the connection.
•If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The speed parameter can adjust itself even if the connected port does not autonegotiate.
Autonegotiation and Network Interface Cards
Problems sometimes occur between the switch module and third-party network interface cards (NICs). By default, the switch module ports and interfaces are set to autonegotiate. It is common for devices like laptops or other devices to be set to autonegotiate as well, yet sometimes autonegotation 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 available from the manufacture.
If the port statistics show excessive FCS, late-collision, or alignment errors, verify that the cable distance from the switch module to the connected device meets the recommended guidelines. See the "Cable and Adapter Specifications" section on page B-2 for cabling guidelines.
Resetting the Switch Module
For a standalone switch, you can perform these functions by using the AMM web interface:
•Reboot the switch
•Restore factory defaults
•Set or reset the IP address, netmask, and default gateway
•Enable or disable external ports
•Enable or disable management through the external ports
•Change or update firmware
For a switch stack, you can use the CLI to perform the same functions. For more information, see the switch module software configuration guide and the command reference on Cisco.com.
Using the Mode Button to Reset the Switch Module
You can use the Mode button to reset a standalone switch module.
For a standalone switch module, resetting the switch module deletes the configuration and reboots the switch module.
For a standalone switch module, use a small pointed object to press and hold the Mode button on the switch module front panel. The switch module LEDs begin blinking after about 3 seconds. Continue holding down the Mode button. The LEDs stop blinking after 7 more seconds, and then the switch module reboots.
The switch module is now unconfigured. You can enter the switch module IP information by following the procedures described in the switch module getting started guide on Cisco.com,
For switch stacks, pressing and holding the Mode button on a member switch module causes the stack to reboot. It does not remove the configuration from any member switch.
How to Replace a Failed Stack Member
If you need to replace a failed stack member, you can hot swap or replace the switch module by following this procedure (only Catalyst 3110 switch modules):
1. Get a replacement switch module that has the same model number as the failed switch module.
2. Disconnect and remove any modules and cable connections.
3. Remove the failed switch module.
4. Install and then connect the replacement switch module to the stack.
If you had manually set the member numbers for any members in the stack, you need to manually assign the replacement switch module with the same member number as the failed switch module. To manually assign the member number, see the switch module software configuration guide on Cisco.com.
5. Make the same Gigabit Ethernet connections on the replacement switch module that were on the failed switch module.
6. Reinstall any modules and cable connections.
The replacement switch module will have the same configuration for all the interfaces as the failed switch module and will function the same as the failed switch module.