Server Losing Connection to AD DC Intermittently

  • Two Windows Server 2012 R2 VMs on the same Hyper-V 2012 R2 host, one is a dedicated Active Directory Domain Controller. The other is an app and file server. There are gobs of resources, this is a way overbuilt host. The physical host has 20 physical cores, 40 virtual threads. The DC has two vCPU assigned. The app server has ten vCPU assigned. Both have plenty of RAM. The DC has 6GB, and the App Server has 64GB. The physical has 128GB. We can't find any constrained resources anywhere.

    From time to time, a few times a day, we get an error from both systems that try to mount drives from the app/file server, and we can see the matching error in that server itself, that connections to the DC have been lost and no DC can be found.

    Screenshot from 2019-04-12 17-00-15.png

    There is only one DC, but having two would likely just hide the problem.

  • Found it. There was a rogue DNS entry for an old domain controller lingering from long ago. So the app/file server would sometimes look up the domain and get the IP of a long dead DC that isn't around.

  • Good find.