I am trying to deploy a VM from a template. This template has been used dozens of times before; nothing special. The problem is that seemingly out of nowhere when I deploy a VM, it's giving it the same MAC address as an existing powered on VM.

Both VMs are using automatic MAC assignment.

It seems that the usual cause for this is having more than 1 vCenter without giving each one a unique ID. Thing is, we only have 1 vCenter.

I have confirmed in the vCenter database, using the following query, that there are no other conflicts in the cluster:


I keep deleting the newly minted VM and trying to re-deploy it, but it gives out the same MAC every time.

When I create a new VM from scratch, it uses a unique MAC.

I can't find any other instances of something like this online, and I can't figure out how this is possible nor what I can do to fix it. I don't want to start assigning MAC addresses manually.


This has gone from a problem that was repeatable to.. not a problem. I don't know what happened or why, but this originally occurred for me on Friday evening, several times. I was able to repeat it this morning before posting this.

Testing now shows unique MACs being generated; no duplicates.

I have no idea why, I'd still like insight if anyone has ideas. I have a sneaking suspicion that this is going to come back. Ugggh.

  • You're using the full templating feature to deploy the VM, rather than cloning it or something aren't you? And are there are no 3rd party tools?
    – Dan
    Commented Aug 3, 2015 at 16:40
  • It is an actual template being deployed, with a customization profile. The new VM has nothing to do with the existing one except that they were from the same template originally. I converted the template back to a VM to see if its NIC had the same MAC as these 2 are getting, but it's different. No 3rd party tools are being used for this deployment. I am using a script to generate IP addresses, but this script receives the MAC address from VMware, so it has no part in generating it.
    – briantist
    Commented Aug 3, 2015 at 16:45

1 Answer 1


I've seen similar issues after upgrading vCenter with old customization profiles, after some version upgrades the profiles become flaky. The usual fix is to just recreate the customization profile from scratch.

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