On ESXi hosts 5.1 and later you can use range-based allocation to include or exclude ranges of Locally Administered Addresses (LAA).
You specify one or more ranges using a starting and ending MAC addresses, for example,(
02:50:68:00:00:FF). MAC addresses are generated only from within the specified range.
You can specify multiple ranges of LAA, and vCenter Server tracks the number of used addresses for each range. vCenter Server allocates MAC addresses from the first range that still has addresses available. vCenter Server checks for MAC address conflicts within its ranges.
When using range-based allocation, you must provide different instances of vCenter Server with ranges that do not overlap. vCenter Server does not detect ranges that might be in conflict with other vCenter Server instances. See the vSphere Troubleshooting documentation for more information about resolving issues with duplicate MAC addresses.