Table Of Contents
Verify the Switch POST Results
Confirm the Switch Connections
Speed, Duplex, and Autonegotiation
Autonegotiation and Network-Interface Cards
Clearing the Switch IP Address and Configuration
Replacing a Failed Stack Member
Locating the Switch Serial Number
Troubleshooting
This chapter describes these topics for troubleshooting problems:
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Clearing the Switch IP Address and Configuration
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Diagnosing Problems
The LEDs on the switch front panel provide troubleshooting information. They show power-on self-test (POST) failures, port-connectivity problems, and overall switch performance. You can also get statistics from the CLI or from an SNMP workstation. See the software configuration guide and the switch command reference on Cisco.com or the documentation that came with your SNMP application for more information.
This section includes these troubleshooting topics:
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Verify the Switch POST Results
As the switch powers on, it begins the POST, a series of tests that runs automatically to ensure that the switch functions properly. It might take several minutes for the switch to complete POST.
When the switch begins POST, the system LED slowly blinks green. When POST completes, the system LED blinks amber. If POST fails, the system LED remains amber. If POST completes successfully, the system LED rapidly blinks green.
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Look at the Switch LEDs
You must have physical access to the switch to do this. Look at the port LEDs for troubleshooting information about the switch. See the "LEDs" section on page 1-4 for a description of the LED colors and their meanings.
Confirm the Switch Connections
Review this section when troubleshooting switch connectivity problems.
Bad or Damaged Cable
Always test the cable for marginal damage or failure. A cable might be sufficient to connect at the physical layer but then cause packet corruption because of subtle damage to its wiring or connectors. You can identify this situation because the port will have many packet errors, or the port will constantly lose and regain link. In these situations:
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Ethernet and Fiber Cables
Make sure that you have the correct cable type for the connection:
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Link Status
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:
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SFP Module Port Issues
Use only Cisco small form-factor pluggable (SFP) modules on the switch. 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. Test these items:
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Port and Interface Settings
Verify that the port or interface is not disabled or for some reason powered down. If a port or interface is manually shut down on one or the other side of the link, the link does not come up until you re-enable the port. Use the show interfaces privileged EXEC command to determine the port or interface error-disabled, disabled, or shutdown status on both sides of the connection. If necessary, re-enable the port or the interface.
Ping the End Device
Test the end device by pinging it 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.
Spanning Tree Loops
Spanning Tree Protocol (STP) loops can cause serious performance issues that might appear to be port or interface problems. In this situation, the switch bandwidth is used repeatedly by the same frames, crowding out legitimate traffic.
A unidirectional link can cause loops. This occurs when the traffic that the switch sends is received by its neighbor, but the switch does not receive the traffic that is sent from the neighbor. A broken fiber-optic cable, other cabling, or a port issue could cause this one-way communication.
You can enable the UniDirectional Link Detection (UDLD) protocol on the switch to help identify difficult-to-find unidirectional link problems. UDLD supports a normal mode of operation (the default) and an aggressive mode. In normal mode, UDLD detects unidirectional links because of incorrectly connected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links caused by one-way traffic on fiber-optic and twisted-pair links and by incorrectly connected interfaces on fiber-optic links. For information about enabling UDLD on the switch, see the "Understanding UDLD" section in the software configuration guide.
Verify the Switch Performance
Review this section when you troubleshoot switch performance problems.
Speed, Duplex, and Autonegotiation
If the port statistics show a large number of alignment errors, frame check sequence (FCS), or late-collisions errors, a speed or duplex mismatch might be the problem.
A common issue with speed and duplex occurs when the duplex settings are mismatched between two switches, between a switch and a router, or between the switch and a workstation or server. This can happen when you manually set the speed and duplex or because of autonegotiation issues between the two devices.
These circumstances can result in a mismatch:
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To maximize switch performance and ensure a link, follow one of these guidelines when you set or change the settings for duplex and speed:
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Autonegotiation and Network-Interface Cards
Problems sometimes occur between the switch and third-party network-interface cards (NICs). By default, the switch ports and interfaces are set to autonegotiate. It is common for devices such as laptop computers or other devices to also be 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, the firmware or software on your NIC might be causing the problem. Upgrade the NIC driver to the latest version available from the manufacturer.
Cabling Distance
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. See the "Cable and Adapter Specifications" section on page B-4 for cabling guidelines.
Clearing the Switch IP Address and Configuration
This section describes how to reset the switch by rerunning the initial configuration dialog (system configuration dialog). These are reasons why you might want to reset the switch:
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Caution
To reset the switch:
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The switch displays the prompt to run the initial configuration dialog. The switch now behaves like an unconfigured switch.
Replacing a Failed Stack Member
If you need to replace a failed stack member, you can hot swap or replace the switch by following this procedure:
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If you manually set the member numbers for any members in the stack, you need to manually assign the replacement switch with the same member number as the failed switch. To manually assign the member number, install the replacement switch and wait for it to boot up. Use the CLI to manually assign the member number (see the software configuration guide for instructions) before you connect the switch to the stack.
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The replacement switch will have the same configuration for all the interfaces as the failed switch and will function the same as the failed switch.
Locating the Switch Serial Number
If you contact Cisco Technical Assistance, you need to know the serial number of your switch. Use these figures to locate the serial number on your switch. You can also use the show version command to get the serial number.
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Figure 3-1 Serial Number Location on the Cisco Catalyst Blade Switch 3130 for Dell
Figure 3-2 Serial Number Location on the Cisco Catalyst Blade Switch 3032 for Dell
