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I expanded the disk space allocated to a Server 2012 Standard virtual machine running on Hyper-V (Server 2016 Standard) and rebooted the VM. Everything appeared to be working fine until the next morning when clients began trying to query Active Directory for various services, none of which worked.
Logging into the server I noticed the little popup in the bottom right corner saying that drive mappings were not successful. Having seen this any number of times, I had not paid any attention to it the previous night, but opening File Explorer, it became clear that none of the drive that map via GPO were present. Uh-oh.
All auto start services were running, DNS looked to be working fine, and NIC setting were unchanged. Event Viewer showed very little, just that Group Policy failed to apply settings, and there was an HTTP Event, and then NETLOGON 5782, no DNS servers. Uh-oh again, this is a domain controller and the only DC in this micro client’s network.
Event 15021 for HttpEvent – An error occurred while using SSL configuration for endpoint 0.0.0.0:443. The error status code is contained within the returned data.
Event 1085 for Group Policy – Windows failed to apply the Group Policy Services settings. Group Policy Services settings might have its own log file. Please click on the “More information” link.
Event 5782 for NETLOGON – Dynamic registration or deregistration of one or more DNS records failed with the following error:
No DNS servers configured for local system.
I ran DCDIAG which reported numerous errors, most of them being Error 64 “The specified network name is no longer available”. The first instance of the error was during the SYSVOL check.
A DCDIAG /test:DNS revealed “Authentication failed with specified credentials”.
I assumed some sort of DNS corruption. I could not imagine that the issue was related to expanding the available disk space on the VM, but I decided to restore from the previous night’s backup. Veeam Instant Restore is a lovely thing and it quickly showed me the exact same problem from that backup. I decided to do another restore from a few days prior when the DC would have been fully functional. The problem still appeared.
I started to get concerned, but I thought about what was common between each of those versions of the same VM. The problem could not have persisted for days when the client had been working without complaint. The commonality seemed to be the reboot, or in the case of the restores, the reboot that occurs because of the restore.
We had a problem a few weeks ago where a virtual legacy NIC assigned to a legacy VM disappeared, and it had to be re-added. This occurred after the Hyper-V host server had updates applied and had been rebooted, but the VMs had not. They went into Saved state and resumed after the host came back up.
Using that experience and a hunch that the Host server had also been recently updated, I removed the virtual NIC from the Server 2012 VM, and added a new one. I assigned the old static IP and DNS to the new NIC and rebooted, and all was working perfectly!
Article By: Jason Knowles