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Alignment error counter increments due to a misconfiguration or physical layer issue

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Core issue

A misconfiguration or a physical layer issue may cause the alignment error counter to increment.

Resolution

Alignment errors are the count of the number of frames received that do not end with an even number of octets and have a bad Cyclic Redundancy Check (CRC). This could indicate a cable problem or a faulty  transmitter on the network equipment connected at the other end. This count should be zero or very low. When the cable is first connected, some alignment errors may occur. Issue the show port command to check for alignment errors on a Catalyst OS (CatOS)-based switch. On a Cisco IOS -based switch, issue the show interface command to check for CRC errors.

To resolve alignment errors, perform these tasks:

  • Test the existing cable with a cable tester or replace it with a known good cable.
  • Hard set the speed and duplex settings if both sides of the link can be hard set.

    On a CatOS-based switch, issue the set port speed and set port duplex commands.

    For example, to set the speed to 100 and the duplex to full on port 3/2, issue these commands:

    set port speed 3/2 100
    set port duplex 3/2 full

       

    On an Cisco IOS-based switch, issue the interface configuration speed and duplex commands. For example, to set the speed to 100 and the duplex to full, these would be the commands:

    Switch(config-if)#speed 100
    Switch(config-if)#duplex full

  • Verify that the NIC has the latest driver and that the driver supports  the  required speed and duplex settings.
  • Verify that no known compatibility issues exist with the NIC. Refer to Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues.
  • Connect the switch port to a different device while using the same cable, and monitor for alignment errors.
  • Move the cable to a different port on the same module, and monitor for alignment  errors to determine if the problem follows the port.
  • Move the cable to a port on a different module, and monitor for alignment  errors to determine if the problem follows the module.

For more information regarding troubleshooting port issues, refer to   Troubleshooting Switch Port Problems.