Manually Assigning a MAC in VMware

During our migration from ESXi 4.1 Update 2 to ESXi 5 Update 1 we decided to change all nics on VMs to VMXNET3.  Everything was fine until my users came in the next morning and couldn’t do some of the things that they needed to do.  It turns out that there were some programs tied to the old MAC address of the nic that I had removed from the virtual machine.  We had to get licenses tied to the new MAC addresses, and then the decision was made for the remaining VMs that I still had to work on, to keep the current MAC address.  How to do this…

1.  Install the latest VMware tools. (If you haven’t done this, you might not see VMXNET3 as an option for network card.
2. RDP into the virtual machine and take not of the IP information on all nics.  Then, change the IP to “Obtain an IP address automatically” and “Obtain DNS server address automatically”.  (This keeps you from getting weird messages later about IP addresses already being assigned to a nic.Image
3.  Shut down the VM.
4.  Edit Settings on the VM using the vSphere Client.
5.  Click on each network adapter and write down the current MAC address.  Then click on remove to remove the nic from the machine.
6.  Click “Add” and then select “Ethernet Adapter”.
7.  Change the adapter type to VMXNET3 and then choose your network for the VM.
8.  Change the MAC to “Manual” and then enter the MAC that you wrote down before from the old nic.
9.  Click “OK” and the old nic will be removed and the new nic added.  If you go back in and look at the nic you will notice that it has the MAC that you manually added.
10.  After powering on your VM, open the command prompt in administrative mode and type without quotes, “set devmgr_show_nonpresent_devices=1”  Then type “devmgmt.msc”
11.  When device manager opens click “View –> Show Hidden Devices”.  Hidden devices, especially old nic need to be removed.  You will see unused devices showing greyed out.  Right click on them and choose “uninstall”.

Hopefully this saves someone from a licensing headache when upgrading your VMs.

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