VMware Virtual MAC Addresses

Mohamed Hamad is a Global Knowledge instructor who teaches and blogs from Global Knowledge Egypt.

Did you ever try to check the vNIC MAC address of your Virtual Machine? Did you ever want to know how it’s generated? Did you ever wonder how VMware ensures the uniqueness of this MAC?

First, ESX/ESXi generates a virtual MAC address automatically to each vNIC in your VMs once you power it on This MAC address is saved in the VM configuration file “.vmx”, and this 6 Byte Virtual MAC is divided into :

  • 3 Bytes for VMware OUI “Organization Unique Identifier”
  • 3 Bytes generated randomly for each vNIC

Regarding the first part of the MAC — First 3 Bytes — VMware OUI, it depends on where you initialize the creation of the VMs, meaning if you created it while connected to the vCenter Server, it will start with 00:50:56. But if you created your VM directly while connected to the ESX/ESXi, it will start with 00:C0:29. This is the reason why we can see when a VM starts with different MAC addresses.

About the second part of the MAC — Second 3 Bytes — and to ensure the uniqueness of the vNIC MAC across the whole environment, the system uses a hash of the below to create it:

  • The Physical ESX/ESXi SMBIOS “System Management BIOS” universally unique identifier
  • The name of the VM
  • The location of the VM
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