I had a strange issue today.

In my lab, I have a hyper-v 2012 R2 cluster with VMM 2012 R2 that i use as a dev/test environment. Among other things, i let this rig take in all patches and what not before doing anything with production systems.

I recently updated the VMM 2012 R2 server and console to UR12. Now, for no apparent reason, I were no longer able to change VLANs for any VM’s.

I only got the following message when changing network on a VM:

The specified VLAN configuration is not valid.

Ensure that the virtual network adapter is connected to a virtual switch, that a valid VLAN ID is specified, and then try the operation again.

ID: 10605

The VM’s that have had VLANs set before work.

So, as i’ve been around a few servers, i usually have a few ideas about where to start looking.

So, i was thinking: Switches work. All VLANs are (still) trunked to all hosts. I could set VLANs manually in hyper-v manager or failover cluster manager, but not in VMM anymore.

No changes have been made to logical switches or vm networks or any config whatsoever.

Next step: Uninstall the lastly installed updates, namely UR12. This update has two parts, KB3209585 and KB3209966. I uninstalled both and one reboot later I am back in business, changing VLANs.

A word of WARNING: If you have also upgraded the VMM host agents on the Hyper-V hosts, you should not uninstall UR12, as it will not be able to communicate with the agents that have been upgraded to the UR12 version (I.E. all your hosts). (Or find a way to downgrade the host agents first).