MAC addresses are generated for virtual network adapters that the service console, the VMkernel, and virtual machines use.

In most cases, the generated MAC addresses are appropriate. However, you might need to set a MAC address for a virtual network adapter, as in the following cases:

Virtual network adapters on different physical hosts share the same subnet and are assigned the same MAC address, causing a conflict.

To ensure that a virtual network adapter always has the same MAC address.

To circumvent the limit of 256 virtual network adapters per physical machine and possible MAC address conflicts between virtual machines, system administrators can manually assign MAC addresses. VMware uses the Organizationally Unique Identifier (OUI) 00:50:56 for manually generated addresses.

The MAC address range is 00:50:56:00:00:00-00:50:56:3F:FF:FF.

You can set the addresses by adding the following line to a virtual machine‘s configuration file:

ethernet<number>.address = 00:50:56:XX:YY:ZZ

where <number> refers to the number of the Ethernet adapter, XX is a valid hexadecimal number between 00 and 3F, and YY and ZZ are valid hexadecimal numbers between 00 and FF. The value for XX must not be greater than 3F to avoid conflict with MAC addresses that are generated by the VMware Workstation and VMware Server products. The maximum value for a manually generated MAC address is:

ethernet<number>.address = 00:50:56:3F:FF:FF

You must also set the option in a virtual machine’s configuration file:

ethernet<number>.addressType="static" 

Because VMware ESX virtual machines do not support arbitrary MAC addresses, you must use the above format. As long as you choose a unique value for XX:YY:ZZ among your hard-coded addresses, conflicts between the automatically assigned MAC addresses and the manually assigned ones should never occur.