2012 R2 DC not reachable

Ralph Scharping
Ralph Scharping used Ask the Experts™
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Hi,

my business and I service about 300 customers in the small business range, mostly with pure Microsoft environments.

Our so far only two customers who run no servers other than Windows Server 2012 R2 experience this problem:

Every now and then, every other day or less frequent, logon into RDS is not possible because no domain controller is available.  DNS service does not work even though the service is running.  The AD member servers log frequent events relating to no DC available.  The DC logs no events, feels just fine, cannot resolve any DNS queries and sits there in ignorant bliss.
Restart of the service does not help, I have to reboot the entire machine .

Both customers run VMware, one has Exchange, the other does not.   Both customers have only one single DC. One domain, one tree.  
Eventlog does not record anything of any help.  

Many other customers run Server 2012 R2 for some services and 2008 R2 for others.  They don't report anything like this.

Does anybody have a clue what might be happening there?  Has anyone experienced something like that?

Thanks,
Ralph
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Both customers run VMware, one has Exchange, the other does not.

Ensure vmware don´t do oversubscription/overcommit memory, focus especially on Exchange setup. I suggest you set fixed memory value.
Ralph ScharpingDigital Therapist

Author

Commented:
Thas is the case.  Memory is not oversubcribed.
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Ralph ScharpingDigital Therapist

Author

Commented:
DNS is already configured as described.
Ralph ScharpingDigital Therapist

Author

Commented:
Yes, no patches available.
Another thing, your DNS is configured to use any kind of router as forwarder?
Ralph ScharpingDigital Therapist

Author

Commented:
No, I am forwarding to google.  But resolving even internally does not work when the issue occurs.
You can try disabling EDNS0, on command prompt run dnscmd /config /EnableEDNSProbes 0
Not requires restarts.
Ralph ScharpingDigital Therapist

Author

Commented:
The command went through without an error message.  But I'll have to wait a few days to check if this changed anything.

Somehow I don't think it is an isolated DNS issue...
kevinhsiehNetwork Engineer

Commented:
Which type of NIC are the VMs using? They should be using Vmxnet3.
Ralph ScharpingDigital Therapist

Author

Commented:
They are not.  Default is E1000 on VMware 5.5 and that's what they are.
Network Engineer
Commented:
Yeah, I think that is your problem. Change to VMXNET3 and things should be a bit better. E1000 is not recommended. If you have VMware support you can also call them, but I have been told that E1000 is not recommended if VMXNET3 is available. I had to switch my VMs too as the default was E1000.
Ralph ScharpingDigital Therapist

Author

Commented:
Thank you for this hint.  I will change that and retry.  But I will need to wait a week to verify if this is really better.
Ralph ScharpingDigital Therapist

Author

Commented:
I'm thinking we might be on the right track here.  Just exchanged the LAN adapters on all VMs.  First thing I notice is MUCH faster logon times...
kevinhsiehNetwork Engineer

Commented:
:-)
Ralph ScharpingDigital Therapist

Author

Commented:
So far so good.  No crashes yet since I made the change.
Ralph ScharpingDigital Therapist

Author

Commented:
Perfect!
I just wonder why the creation of a new VM defaults to E1000.
No trouble since I changed it....
Thanks a million!

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