MAC address is not retained using the "Retain MAC" option after migrating a virtual machine using HCX within the same VC (Single vCenter Operation)

Products

• VMware HCX

Issue/Introduction

• You are migrating a virtual machine using HCX Bulk Migration or Replication Assisted vMotion (RAV) within the same vCenter (Single vCenter Operation) and have selected the "Retain MAC" option.
• Note: This issue only affects Single vCenter Operations, where the source and target VM are on the same vCenter, but are being migrated between different clusters.
• Post-migration, you observed that the MAC address for the migrated VM (target) was not retained, and the virtual machine received a new MAC address.
• From vCenter logs (/var/log/vmware/vpxd/vpxd.log), the following error is observed: info vpxd[...] VM has conflict mac [00:50:##:##:##:##] with existing, new mac [00:50:##:##:##:##].

Environment

VMware HCX

Cause

In a single vCenter environment, vCenter cannot register two VMs with the same MAC address. This triggers a conflict in the following ways:

• For RAV (Replication Assisted vMotion): During the delta sync phase, HCX registers a "shadow VM" on the destination host while the source VM is still active. vCenter detects this temporary overlap as a conflict. If the adapter is set to Automatic, vCenter registers the conflict and forces a new MAC address assignment during the next power cycle.
• For Bulk Migration: The source VM remains in the vCenter inventory (in a powered-off state) while the new VM is brought online at the destination. Because the original VM still "owns" the MAC address in the vCenter database, the destination VM is forced to take a new MAC address to resolve the duplication.

Resolution

This is a known issue impacting VMware HCX.

Workaround

To ensure the MAC address is retained during a Single vCenter Operation:

1. Before starting the migration, edit the Virtual Machine settings.
2. Navigate to the Network Adapter configuration.
3. Change the MAC Address assignment from the default Automatic to Manual.
4. Once the VM is migrated, the MAC address will remain the same as the source, as vCenter will not attempt to re-assign a manual entry.

Additional Information

Understanding VMware HCX Bulk Migration

Note: In a single vCenter RAV migration a UUID conflict is reported which results in a new vCenter instance UUID (vc.uuid) being assigned to the migrated VM.