Virtual Port Channel (vPC) and Link Aggregation Control Protocol (LACP) Troubleshooting

Introduction

This tutorial covers troubleshooting Virtual Port Channel (vPC) and Link Aggregation Control Protocol (LACP) on Cisco Nexus switches. Understanding how to identify and resolve common issues with vPC and LACP is crucial for maintaining a stable network environment. This guide will walk you through essential troubleshooting steps to ensure your configuration is correct and functioning properly.

Step 1: Verify Feature Activation

• Log in to both Nexus switches.
• Check that vPC and LACP features are enabled by running the following command:

  show feature | exclude disabled
  

• Ensure both features are listed as active.

Step 2: Check IP Reachability

• Confirm that the control link between the switches is operational:
  • Use the command to check the interface configuration:

    show running-config interface ethernet 1/1
    

  • Ping the IP address of the peer switch using the correct VRF:

    ping 10.11.12.11 vrf keepalive
    

• Verify that the ping is successful, indicating proper reachability.

Step 3: Validate vPC Configuration

• Check the vPC configuration for keepalive settings:

  show vpc
  

• Ensure that the keepalive destination and source IPs are configured correctly.

Step 4: Inspect Port Channel Status

• Check the status of the port channel:

  show port-channel summary
  

• Look for any interfaces marked as "suspended" (indicated by an "S"). This may indicate issues in the configuration.

Step 5: Review Individual Port Configuration

• Verify the configuration of each port in the port channel:

  show running-config interface ethernet 03
  

  • Ensure LACP mode is set correctly (active or passive).
  • Check that the channel group matches the port channel number.

Step 6: Reactivate the Port Channel

• Sometimes, bringing the port channel down and back up can resolve suspended states:

  interface Port-channel 25
  shutdown
  

  no shutdown
  

• This forces the port channel to reinitialize and can clear any inconsistencies.

Step 7: Analyze Logs for Errors

• Check logs for any error messages related to the port channel:

  show logging
  

• Look for messages indicating why a port might be suspended or not coming up.

Step 8: Ensure All vPCs are Configured

• Verify that all relevant vPC configurations are present on both switches:

  show vpc
  

• Ensure that the number of configured vPCs matches on both Nexus switches.

Step 9: Check Interface Status

• Inspect the status of individual interfaces within the port channel:

  show interface status
  

• Look for any interfaces that are down or suspended.

Conclusion

In this tutorial, we covered essential troubleshooting steps for resolving issues with vPC and LACP on Cisco Nexus switches. Key actions include verifying feature activation, checking IP reachability, validating configurations, and reactivating port channels. By following these steps, you can effectively troubleshoot common issues and maintain a stable network environment. For further learning, consider exploring more advanced topics in vPC and LACP configurations.