Automatic Virtual Machine Activation (AVMA) is the one Hyper-V feature in the Datacenter edition of Windows Server that you won’t find in the other versions (Standard or Hyper-V Server). This is a technical feature than enables a licensing feature. Hosts that are licensed with the Datacenter edition are entitled to host as many VM installations of Windows Server as you are able to get on to that licensed physical machine. The complication for larger or hosting companies is activating the installations: firewalls and NVGRE network virtualization (SND or software-defined networking) makes routing to Microsoft’s clearing house or a KMS a little difficult. So Microsoft allows you to activate the host, and install AVMA keys into the guest OS of your template virtual machines.

Microsoft has published a KB article that is related to a funny you might see in your virtual machines that is related to AVMA. 


On a Windows Server 2012 R2 Datacenter Hyper-V host, you may see 2 unknown device under Other Devices in device manager of any virtual machine running operating systems earlier than Windows Server 2012 R2.
If you view the properties of these devices and check driver details, Hardware IDs or Compatible IDs, they will show the following:

  • vmbus{4487b255-b88c-403f-bb51-d1f69cf17f87}
  • vmbus{3375baf4-9e15-4b30-b765-67acb10d607b}
  • vmbus{99221fa0-24ad-11e2-be98-001aa01bbf6e}
  • vmbus{f8e65716-3cb3-4a06-9a60-1889c5cccab5}


These Virtual Devices (VDev) are provided for Automatic Virtual Machine Activation (AVMA) to communicate with the host. AVMA is only supported on virtual machines running Windows Server 2012 R2 or later versions of operating systems.

According to Microsoft the unknown devices are “harmless and can be ignored”. Hosting companies might want to add this one to their customer knowledgebase. In my experience, this is one of those little annoying things that will create annoying and time consuming helpdesk calls.

4 comments so far

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  1. I had this problem in (i think server 2008 r2) VM that is running on Server 2012R2.
    If you bored with that yellow mark, you can do the following:

    On that VM insert integration Service setup disk. Open it and go to supportamd64 and find “Windows6.2-HyperVIntegrationServices-x64 (cabinet file). Use 7 zip to extract cabinet file.
    Go to device manager and point unknown device to search driver in just extracted folder.

    That’s it

  2. This also occurs with 2012 R2 Standard as the host, when using the Microsoft Virtual Machine Converter v2 (MVMCv2) to create the guest. Updating the drivers as per Marko’s comment works.

  3. this also happens in 2012 R2 Standard as the host and windows 2008 R2 Ent P1 as VMs.

    very annoying but thank you for the fix Marko

  4. Thanks Marko, you are the best.

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