Hyper-V guests - loss of network connectivity requiring reboot of Hyper-V host.

realtimer used Ask the Experts™

I have recently introduced a Windows 2012R2 Hyper-V host server (Version 6.3.9600.16384).  This server hosts 2 Windows 2012R2 guest machines, one which will be a domain controller & file share, whilst the other will be the Exchange 2013 server.  The server is not in full production yet but will be soon.  

Early this morning we found that the guest Operating Systems no longer had network connectivity.  I could not ping them from any other machine on the network.  However the guest machine were able to ping each other.  Once I restarted the host server all network connectivity was back to normal.  

I checked the Event Viewer on the host server but was unable to find any Events that corresponded to this.  EV was quite clean.  Consequently I am unsure as to how to determine what could have caused the issue.  This would be the time that I can take any proactive action to prevent a full outage once the servers are in full production.

Any suggestions as to what I could look for?  What could cause this sort of thing?  This is the first time I have encountered this in the last 2 weeks since the servers have been put in place.

Any suggestions would be greatly welcome.

Thanks in advance.


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Some basic troubleshooting first of course.  As far as your setup for your virtual switch manager, is the connection type set to External network, or Internal Network?  It should be set to External Network if not already.

Does your host server have at least two LAN cards?  If so, one should be for the host OS and the other should be dedicated to the virtual OSes.  The checkbox for Allow management operating system to share this network adapter should be unchecked so that the host does not share this adapter.

It could be a faulty cable, so you might try switching that out.  Check for any driver updates to the LAN card that is used for the virtual OSes.
Distinguished Expert 2018
The issue mostly happens if host network adapter device drivers are not stable / network card firmware is out of date and not compatible with latest host OS
You should check server vendor website / ask server vendor for any network firmware updates / stable device drivers for your host OS version

Before restarting the host (This should be the last step) you should try disabling / enabling host adapter followed by guest adapter

Also as highlighted by others, you should have dedicated NIC for virtual machine to help isolate issue

One option could be you could deploy Hyper-v 2012 R2 failover cluster which have ability to detect host LAN card failure and in that case it will failover all VMs to other host
Since your environment is small, it might be expensive / overkill to get 2nd physical server along with SAN / NAS storage to build failover cluster

The best option could be you can go for O365 hosted email services for small user base which will eliminate need for maintaining exchange onpremise
We were able to locate the issue.  This was a Dell server.  We had to change the following setting on the NIC that was supporting the Virtual Machines.
Device Manager | Network Adapter (Properties)| Advanced | Virtual Machine Queues (Change to DISABLED).

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