I was originally made aware of this issue last Thursday. No major changes happened last week.

I am unable to add ESXi hosts to our domain, unable to log in using Windows credentials, unable to setup AD authentication in our vCenter appliance.

This was all working for years.

No recent patches installed to the AD domain controllers/DNS servers, no infrastructure changes made, no relevant DNS records modified/deleted, no recent patching to the VMware systems.

I am unaware of any AD issues other than with these VMware systems.

I also noticed that intermittently I cannot log on to them as Root either. I am forced to connect via SSH, run DCUI, and restart the Management Agents. Sometimes this helps, sometimes not.

Checked time, they're all in sync.

I haven't done anything with disabling TLS.

Our AD servers are a mix of 2008 R2 and 2012 R2.

vCenter is v 5.5.0 build 4180647

Hosts are a mix of 6.0.0 build 4600944, 5.5.0 build 4722766 (except for the one I reverted back to build 3029944 to test if it was the build causing the issue), and 5.0.0 build 3982828.

Also, only 3 systems are managed by vCenter currently, all the others are stand-alone

I'm at a complete loss as to what's going on.

Any and all help is greatly appreciated.