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Since some days for a customer of mine Hyper-V requires static MAC addresses to be assigned. Starting a VM with a dynamic MAC address results in a start errir; "No available MAC address for network adapter".

Point is - that worked perfectly until some days ago and there are not enough VM's on that host to actually run out of MAC addresses AND I can change what I want in the MAC address pool, the error does not go away (I have it now for 4096 mac addresses and the machine has not even 30 vm's with a total of maybe 34 NIC's). A new VM I created for test purposes shows all 0's for MAC addresses and then fails to start.

All that we did was install DPM for a test..... can this be related to DPM#s backups?

The software is a current 2012 R2 with all patches installed.

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Just to be sure the range is set properly, check the registry keys under HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization? –  Grant Apr 28 at 4:28
    
They seem to e set correctly - 00 15 5d c8 80 00 min and max is 00 15 5d c8 8f ff - that is plenty of MAC addresses. –  TomTom Apr 28 at 4:34
    
Another key of interest is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\Worker\CurrentMacAddress which should have the next available mac address to use. Does flipping the vm to static then back to dynamic help? –  Grant Apr 28 at 4:37
    
It does not help. And CUrrentMAccAddress is set to 00 15 5d c8 80 00. Heck , I was doing some patching yesterday and machines did not restart when needed - they stayed off because of this error. Had to manually set them to static, then boot them. –  TomTom Apr 28 at 4:53

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