We have two hosts. On one of the hosts I needed to edit a machine (change the processor configuration). When I powered it down, the entire host seemed to lock up. All guests on that host showed as "disconnected" and the host itself showed as "not responding". I ended up having to reboot the host to get everything back the way it was. I figured it was a fluke, so I tried again and got the same results. The vCenter server is on the other host and there is another AD controller and DNS server running on the other host. So I assume that isn't the issue. Skip forward to today. After hours I started powering down guests on the problem host one by one. No issues. The last one left up was the one I was originally trying to fix. When I powered it down, the host become unresponsive in vCenter. And this time the entire vCenter was unresponsive. Even in the appliance manager which looked fine, certain tabs like Authentication didn't work at all. I'm not sure what it is about that particular guest that is causing the problem.

The guest in question is a Windows Server 2012 server running our AD and DNS. There are other AD and DNS servers elsewhere on the network.

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    What DC/DNS server are your hosts and vCenter using? – GregL Feb 23 '17 at 1:12
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    You nailed it. It was DNS on the hosts themselves. I had been looking all over vCenter and my network config. Turned out I only had one DNS entry in the host's network setup. Thank you. – MSCF Feb 23 '17 at 15:36
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    Lucky guess. I just answered with a little more detail, so feel free to throw me a check if you want :). – GregL Feb 23 '17 at 16:52

I'd recommend checking the DNS settings on both the vCenter and the hosts, since losing the ability to resolve DNS would likely cause the hosts to appear to drop off the network.

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