When you move a virtual machine between vCenter Server instances, the environment specifically handles MAC address migration to avoid address duplication and loss of data in the network.

In an environment with multiple vCenter Server instances, when a virtual machine is migrated, its MAC addresses are transferred to the target vCenter Server. The source vCenter Server adds the MAC addresses to a black list so that it does not assign them to newly created virtual machines.

To reclaim unused MAC addresses from the black list, contact VMware Technical Support for assistance.