Virtual MAC address assignments are based on Microsoft’s organizationally unique identifier (OUI) registration with the Institute for Electrical and Electronic Engineers (IEEE). An OUI is a unique MAC address prefix assigned that is assigned to all NIC vendors, both physical and virtual.

VMware Organizationally Unique Identifier (OUI) allocation uses the default OUI 00:50:56 as the first three bytes of the MAC address generated for each virtual network. The MAC address-generation algorithm produces the rest of the MAC address. The algorithm guarantees unique MAC addresses within a virtual machine and attempts to provide unique MAC addresses across virtual machines.

The VMware Universally Unique Identifier (UUID) generates MAC addresses that are checked for conflicts. The generated MAC addresses are created by using three parts: the VMware OUI, the SMBIOS UUID for the physical ESXi machine, and a hash based on the name of the entity that the MAC address is being generated for. All MAC addresses that have been assigned to network adapters of running and suspended virtual machines on a given physical machine are tracked.

So if you are trying to use some other Mac Address (of range 00:0c:29) for your VM other than dynamically generated by VMware, then at the time of VM startup you will get error as shown below:

In Esxi 5.5 new policies have been added where the statically assigned MAC addresses can only be in the range 00:50:56:xx:xx:xx series, If you try to change it to something else and then power on the guest machine, you may see above error.

Resolution:

This issue can be resolved by changing the value of parameter “ethernetX.checkMACAddress = “false””

Note: Replace X with ethernet number for e.g ethernet1

Following is an sample of working .vmx file for static mac address.

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