Changing the MAC Address of a Virtual Machine

VMware ESX Server automatically generates MAC addresses for the virtual network adapters in each virtual machine. In most cases, these MAC addresses are appropriate. However, there may be times when you need to set a virtual network adapter’s MAC address manually — for example:

You have more than 256 virtual network adapters on a single physical server.
Virtual network adapters on different physical servers share the same subnet and are assigned the same MAC address, causing a conflict.
You want to ensure that a virtual network adapter always has the same MAC address.

In order to work around both the limit of 256 virtual network adapters per physical machine and possible MAC address conflicts between virtual machines, the MAC addresses can be assigned manually by system administrators. VMware uses a different OUI for manually generated addresses: 00:50:56. The addresses can be set by adding the following line to a virtual machine’s configuration file:

ethernet0.address = 00:50:56:XX:YY:ZZ

where XX is a valid hex number between 00 and 3F and YY and ZZ are valid hex numbers between 00 and FF. The value for XX must not be greater than 3F in order to avoid conflict with MAC addresses that are generated by the VMware Workstation and VMware GSX Server products. Thus the maximum value for a manually generated MAC address is

ethernet0.address = 00:50:56:3F:FF:FF

VMware ESX Server virtual machines do not support arbitrary MAC addresses, hence the above format must be used. So long as you choose XX:YY:ZZ so it is unique among your hard-coded addresses, conflicts between the automatically assigned MAC addresses and the manually assigned ones should never occur.