Prefix-based allocation allows you to specify an OUI other than the VMware default 00:50:56. This scheme is supported on ESXi hosts 5.1 and later.

You can also choose to use a Locally Administered Address (LAA) instead of OUI, which increases the range of MAC addresses. The MAC address-generation algorithm produces the rest of the MAC address. The algorithm guarantees unique MAC addresses within a machine and attempts to provide unique MAC addresses across machines.

When using prefix-based allocation, you must provide unique prefixes for different vCenter Server instances. vCenter Server relies on different prefixes to avoid MAC address duplication issues.