I'm facing a situation with my Domain Controller that's running Windows Server 2019 and also serving as a DNS server. After moving this VM to a different ESXi host, some of my domain clients aren't able to resolve DNS properly anymore. On these affected clients, the DNS server shows up as 'Unknown', even though the IP (192.168.0.128) is correct and reachable.
When I run `nslookup`, it still indicates 'Unknown' for the DNS server, and while queries for valid internal records (like `vcenter.local`) return an 'NXDOMAIN' error, the same queries work fine on other systems. All my ESXi hosts and VMs are on a vSphere Distributed Switch, and everything is connected without VLANs or isolation rules; it's a flat network managed through a UniFi Dream Router.
Infrastructure components like vCenter and Active Directory Certificate Services are on a different switch that seems to be functioning properly, while the problematic clients are linked to a UniFi Switch Lite. Notably, a Docker host on the same Switch Lite is not having any issues communicating with Active Directory and resolving DNS.
During the VM migration, my Domain Controller rebooted unexpectedly because it is set to reboot daily at 03:00. Problems only started occurring after that reboot. To clarify, affected clients can reach the DNS server by IP, yet they still get 'NXDOMAIN' responses. I've checked everything I can think of, from `dcdiag` to client resolver settings, and everything shows no errors. I'm trying to figure out if this could be related to client-side DNS behavior or possibly an issue with how Windows DNS services handle states after unplanned reboots.
3 Answers
Have you considered reverting the VM back to an earlier snapshot before the migration? It sounds like the migration might have caused some hiccups, and reverting could be a quick fix while you troubleshoot further.
Since the clients on the UniFi Switch Lite are the only ones affected, have you tried clearing the ARP table on that switch? Sometimes stale ARP entries can cause odd connectivity issues. It might be worth a shot!
It could also be useful to examine the DNS suffix search list on the client machines. Misconfigurations there can lead to resolution problems with internal domains. Just a thought!
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