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Issue with intermittent Outlook disconnects from Exchange 2016 Server

I'm in the process of upgrading  servers on a single domain.  The old servers were physical 2008R2 servers with Exchange 2010 on the primary controller.  The new servers are 2016 Standard VMs running on Hyper-V.  Exchange is on one VM and the Domain Controller is on another VM with DHCP as well.  There is an additional VM that is the backup Domain Controller.  Since migrating to 2016 and decommissioning the 2010 server, the network workstations with Outlook (2010 to 2016) experience intermittent disconnects from Exchange Server 2016.  There are 27 workstations on the network with another 10 connecting remotely and another 50 mobile devices that access the exchange email server.  I've opened a Microsoft Support Ticket however they have not been able to resolve the issue in 3 weeks.  We see error 26 in the client event log when the disconnect occurs however there is no other loss of connectivity across the network or internet.  Typically we can resolve the issue by performing an ipconfig /release and ipconfig /renew however occasionally a reboot is required.  DCDIAG is clean other than syslog errors.  Replication is occurring without errors as well.  Thanks for your help.
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kboller
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kboller
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3 Solutions
 
MAS (MVE)Technical Department HeadCommented:
Hi kboller,
Is this happening for Exchange 2010 users or for both?
Exchange 2010 users uses different protocol not like Exchange 2016 users.

Make sure your Exchange 2010 users connect to Exchange 2016 server. Exchange 2016 will proxy/redirect the request to Exchange2010. If this happens to Exchange 2016 users please make sure virtual directories configured properly, Specially RPC/MAPI.
http://www.mustbegeek.com/configure-external-and-internal-url-in-exchange-2016/

Thanks
MAS
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kbollerAuthor Commented:
Thanks MAS.  The 2010 Exchange server has been decommissioned and is no longer on the network.  I'll double check the virtual directories.
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J SSenior Systems AdministratorCommented:
Are you load balancing to your exchange servers?  Have you check the Domain controller performance or exchange performance?
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kbollerAuthor Commented:
We just have the one exchange server and it seems to be coasting at this point along with the domain controllers.  Do you have anything you'd recommend to test the performance on those systems?
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J SSenior Systems AdministratorCommented:
I'd start with using ExPrefWiz to collect the Exchange performance for a few hours during production, then use PAL tool to generate a report  with the logs collected.

ExPrefWiz
https://github.com/Microsoft/ExPerfWiz

Batch file command I personally use to execute the script
\experfwiz.ps1 -duration 02:00:00 -interval 5 -filepath C:\Scripts\ExPerfwiz

PAL Tool
 https://github.com/clinthuffman/PAL
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kbollerAuthor Commented:
Thanks JS, I'll start the collection and let you know how it goes.

MAS, I looked at the Virtual Directories and everything looked good.  We have Split-Brain DNS configured and everything was pointing to the same and correct directories except for a few that Microsoft Support changed to the local name of the exchange server.  Those are ecp, owa, powershelland server active sync.
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MAS (MVE)Technical Department HeadCommented:
Please open outlook with /rpcdiag switch (i.e. type "outlook.exe /rpcdiag") and look for any auhentication issues/errors.

Please try to test Email configuration/URLs configured
Please check step 8 in this article to test email configuration. Type user and password of the problematic user.
https://www.experts-exchange.com/articles/13676/Out-Of-office-not-working.html
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kbollerAuthor Commented:
Thanks MAS, I'll do the testing asap.  There was something that stood out with the certificates.  Attached is the output from Step 4.  I enabled the specified services on the EmailSvr Certificate however am wondering if the wildcard certificate is an issue?  We have only had the disconnect issue with local workstations.  To my knowledge there are no disconnect/connectivity issues with remote devices.
Certificate-Settings.jpg
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MAS (MVE)Technical Department HeadCommented:
Wild card certificate will not create issues for Exchange configured outlooks.
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kbollerAuthor Commented:
J S, it does look like there are resource issues.  Over a 1 hour period right before lunch time, there were 3 periods where processor utilization was over 50% (55 - 72) and one where it was over 80% (87).  Correct me if I'm wrong but it looks like I need to add virtual cpu's to that vm.  There were also many alerts for TCPv4 connection failures.  Would that be related to the high cpu utilization or something related to the network adapter configuration?
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kbollerAuthor Commented:
I think I may have found the issue.  I was able to work on a system today that was currently disconnected.  I opened Outlook with the /rpcdiag switch and it was showing under the error column it showed "auth".  I checked the dns server settings and saw where the isp's dns server was second in the list above the secondary domain controller so I removed the isp's dns server leaving just the two local dns servers.  Immediately Outlook was able to reconnect on its own.  So I've updated the dhcp server to only give out the local dns servers and put ipconfig /release and ipconfig /renew commands in the login script.  We'll have everyone reboot and see if that corrects the issue.  I'll post results after a couple of days to confirm if that corrected the issue.
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kbollerAuthor Commented:
Running Outlook with the /rpcdiag switch provided the most insight into the issue which has been resolved by updating the DNS servers to the local domain controllers running dns.  Also doing the performance monitoring pointed to an issue with the number of CPUs allocated to the VM running Exchange.  Increasing that helped that system's performance as well.
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