How to force VMware to regenerate a MAC address for a virtual machine (or guest OS).

  1. Shut down the Guest OS.
  2. Open up the .vmx file.
  3. Delete the following lines (that begin with…):
    ethernet0.addressType
    uuid.location =
    uuid.bios =
    ethernet0.generatedAddress =
    ethernet0.generatedAddressOffset =

     

  4. Boot up the Guest OS again, and it should generate new details in the vmx file (I’d check afterwards to be doubly sure).

 

The most common scenario for wanting to do this is if you’ve used a “template” Guest OS and copied it to multiple PCs, but accidentally clicked “I moved this Virtual Machine” rather than “I copied this Virtual Machine” when first booting the Guest OS in something like VMware Player.

If you tell VMware that the Guest OS was copied, it automatically generates new UUID info and MAC addresses. If you tell VMware that you moved the Guest OS, all unique identifiers are left alone (including the MAC address). By performing the steps above, you can get VMware to generate you some new, unique identifiers, and stop weirdness on your network 😉

Written by Phil Wiffen

Phil is an IT Professional working in Cambridge, England. He generally blogs about useful solutions that he comes across in his work/play.

13 Comments

atomsnine

Hi Phil,

The procedure you detailed above works correctly. I shutdown the guest, delete the MAC and UUID info, save the change, restart and the entries are regenerated. My problem remains however – The entries generated are identical to the previous.

I have two vm’s that have identical MAC’s and UUID bios info.

As you eloquently stated – I am experiencing some network weirdness because of the duplicate MAC. Ideas?

Phil Wiffen

atomsnine: From memory, if you move one of the VMs in the host’s filesystem, and then open it up in VMware Workstation it should ask you whether you moved it, or whether you copied it. If you say you copied it, it’ll make new a new UUID and hopefully a different MAC too!

Paul Rowley

Hi Phil,

Found this article, however…..

What I need to do is assign a static mac address, is this possible in VMware player? and if so how?

Thanks,

Paul

Phil Wiffen

Try this….

Edit the .vmx file and locate the following generated MAC address:

Ethernet0.addressType =
and
Ethernet0.generatedAddress =

Change the value for ethernet0.addressType from “vpx” to “static”

Change ethernet0.GeneratedAddress to ethernet0.Address

Change the current MAC to a MAC address in the following range:
00:50:56:00:00:00-00:50:56:3F:FF:FF

I got the instructions from here: http://virtrix.blogspot.com/2007/04/vmware-configuring-static-mac-address.html

Tobias

Thanks for sharing this. I made a linked clone (of a linked clone) with Workstation 7 and for some reason it did not generate new uids/macs.

Regards, Tobias

Randy

I screwed it up in exactly the way you described and your fix worked perfectly. You’d think that VMWare would recognize the duplicate MAC’s and give you the option to force a generated instead of just posting an entry to the log…

Thank you very much for the information.

Randy

Farooq Ahmed

Hi,
Worked for me. Did fail first time when i did a overwrite of the modifies .vmx file, but then when i deleted the old file (Make a backup before u delete it) and then copied over the new modified file, it worked wonders.

Thanks again.

Farooq Ahmed

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