Transitioning vDS LACP Negotiation Mode to Active

Products

• VMware vCenter Server

Issue/Introduction

When using a Link Aggregation Group (LAG) on a vSphere Distributed Switch (vDS), you may need to change the LACP negotiation mode from Passive to Active. This is often required to align with physical switch configurations (such as Cisco Nexus 9000 series) to ensure a robust, bilateral negotiation state.

Customers may express concern regarding potential network impact, packet loss, or link flaps during this transition. While the bundle may function in a "Passive-Active" state (where the physical switch initiates negotiation), moving the vDS to Active enables the virtual switch to actively send Link Aggregation Control Protocol Data Units (LACPDUs).

Environment

 

• Product: VMware vSphere / VCF

• Component: vSphere Distributed Switch (vDS) 6.x, 7.x, 8.x

• Physical Infrastructure: Cisco Nexus 9000 Series (or similar LACP-capable switches)

Cause

In a Passive configuration, the vDS only responds to LACP negotiations rather than initiating them. Transitioning to Active mode ensures that both the virtual and physical members of the link actively maintain the health of the LAG. This reduces the risk of the bundle failing to initialize if the physical switch configuration changes.

Resolution

The transition from Passive to Active negotiation is typically a hitless change, but it should be performed with caution.

1. Perform a Backup: Ensure you have a recent backup of your vCenter Server and the vSphere Distributed Switch configuration before making global networking changes.

2. Schedule a Maintenance Window: Although this change is generally transparent to existing traffic, it is a best practice to perform configuration alignment during a scheduled maintenance window.

3. Update LACP Mode:

   • In the vSphere Client, navigate to the Distributed Switch.

   • Select the Configure tab and click on LACP.

   • Select the specific LAG and click Edit.

   • Change the Mode to Active.

   • Set the LACP Timeout Mode (Slow or Fast) to match your physical switch requirements.

4. Verify Configuration:

   • Monitor the physical switch ports. For Cisco Nexus, use the CLI command: show port-channel summary

   • Ensure all member ports remain in a bundled (P) state.

Additional Information

• Note on Active-Active State: This results in an "Active-Active" negotiation state, which is a standard and supported configuration.

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