VMware Organizationally Unique Identifier (OUI) allocation assigns MAC addresses based on the default VMware OUI 00:50:56 and the vCenter Server ID. Prefix-Based MAC Address Allocation On ESXi hosts 5.1 and later, you can use prefix-based allocation to specify an OUI other than the default one 00:50:56 by VMware, or to introduce Locally Administered MAC Addresses (LAA) for a larger. When a virtual machine is powered on, VMware Workstation automatically assigns each of its virtual network adapters an Ethernet MAC address. MAC stands for media access control. A MAC address is the unique address assigned to each Ethernet network device. The software guarantees that virtual machines are assigned unique MAC addresses within a given host system.

I think we are all familiar with the manual MAC address issue - some software depends on the MAC for licensing, and in VMware you need to stick to a certain range of Ethernet addresses if you want to be able to manually put in your own MAC address.

Somehow I think that should have been written in big, bold letters before I started virtualizing a couple of years ago. I'm pretty sure it wasn't mentioned in the class, either. I have several apps that generate their license based on a server's MAC. And yes, now I have to change virtual NICs on several VMs from either Flexible or E1000 to VMXNET2.

Currently running vSphere 4.1, ESX build 320092 across the board.

Since I didn't plan ahead far enough to manually put in those MAC addresses, now I have no choice but to find some way to keep them until the vendors can regen the licensences.

So, here's the procedure I'm using to keep the MAC address:

1) Write down the old MAC

2) Replace Flexible NIC with VMXNET2

3) Unregister the VM

4) Edit the .vmx file and replace the automatically assigned MAC address with the old MAC address

- this is how I get around the GUI

5) Re-register the VM with the host

6) Boot up

So far it has worked for me just fine on two test servers. The question is: Will this cause any problems down the road?

I am currently running a 'vanilla' network setup - no distributed vSwitches. However I do plan on putting that in place later this year, and that's where I'm not sure it my little procedure will come up to surprise me at that point.

You can change the power-on connection setting, the MAC address, and the network connection for the virtual network adapter configuration for a virtual machine.

Required Privileges:

Virtual machine.Configuration.Modify device settings for editing the MAC address and network.

Vm Manual Mac Address Port Id Card

In the vSphere Client inventory, right-click the virtual machine and select Edit Settings.