HCX migration extended option to retain a VM's mac address does not function.

Products

• VMware HCX

Issue/Introduction

The option to retain a mac address when preparing a mobility group and VM for migration will ensure that the mac address that the VM has on the source vCenter will be the same when the VM is instantiated on the destination vCenter. 

 

Environment

HCX

VMware Cloud on AWS

Cause

Despite the option being set in the UI prior to a migration, once the VM is powered on and initialized at the destination datacenter, the VM may not retain the mac address for the following reason:

• The same VM had been migrated previously during mobility migration testing with the retain mac extended option and remains in the destination vCenter. If a forward migration is done twice for the same VM and the first iteration of the VM still remains on the destination vCenter, this issue will occur.
• This occurs because despite the first iteration being done, even if the VM is powered off, or re-named, the vCenter database (VCDB) will hold the mac address. Since the mac address is held, when the second forward migration is done the VM will not be able to retain the same mac because it already exists in the VCDB.

commands/journalctl_-b--0.txt:2828115:Oct 11 16:58:17 ###VM-Name-1### vpxd[47258]: Event [2336094] [1-1] [2025-10-11T16:58:17.575363Z] [vim.event.VmMacConflictEvent] [error] [] [vCenter-comp-DC] [2336094] [The MAC address (00:50:56:##:##:##) of ###VM-Name-1### conflicts with MAC assigned to  ###VM-Name-2###

Resolution

If a second forward migration for the same VM is done and the retain mac address option is desired, the below options are necessary to ensure success:

• Remove the initial forward migration from the vCenter inventory at the destination vCenter prior to beginning the second forward migration
• Change the mac address of the initial forward migration via the vCenter UI. Select the VM from the inventory pane --> select Actions --> select edit settings --> Remove the adapter associated with the mac address in question --> select add new device --> select network adapter --> connect the new network adapter to the same/original port group or NSX-T segment.

Please see this KB for further guidance: Changing the MAC address of a hosted virtual machine