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Server 2016 Hyper-V Virtual Switch Guests Unreachable

    Question

  • We had an issue today with all 11 guests on one of our Hyper-V servers becoming unreachable on the network at once.  All the guests are connected to the same external network virtual switch that isn't shared with the management operating system.  The guests are a mix of Server 2012 R2 standard, CentOS 7, and one Server 2008 R2 guest.  There were no apparent problems with the connectivity to the Hyper-V host server.  

    I changed the config on one VM to disconnect it from the virtual switch, applied the config for the VM, and reconnected it to the same virtual switch.  That got that guest back online, as well as every other guest on that host.  


    I can't find anything of consequence the event logs to indicate a problem.  All I see is the disconnected and reconnected event in the "Hyper-V-SynthNic - Admin" log.  

    It's as though the arp table on the virtual switch stopped working and was then brought back to life by disconnecting and reconnecting the one guest.  

    Anyone familiar with what might be behind this hiccup?

    Thursday, February 16, 2017 10:04 PM

All replies

  • Hi Utegrad,

    >>We had an issue today with all 11 guests on one of our Hyper-V servers becoming unreachable on the network at once.

    Did you make any changes before the issue happen?

    >>I changed the config on one VM to disconnect it from the virtual switch, applied the config for the VM, and reconnected it to the same virtual switch.  That got that guest back online, as well as every other guest on that host.

    The issue seems to be random.

    Try to update the nic driver on host. Then delete and recreate the virtual switch, check if the issue happen again.

    Best Regards,

    Leo


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    Friday, February 17, 2017 2:10 AM
    Moderator
  • Have you turned off all power management of the NIC on which the virtual switch was created?  Issues have been noted in this forum about problems when a NIC is configured with power-saving options.

    . : | : . : | : . tim

    Friday, February 17, 2017 12:27 PM
  • Hi,

    Power management on the NIC as Tim mentioned above should be disabled along with VM Queue in advanced settings on the NIC unless you are using a 10GB network cards with hardware acceleration as this can also cause network interruption / issues.

    Friday, February 17, 2017 1:16 PM
  • Thanks for the replies.  This happened twice today.  Will check the power management, driver, and VM queue and update the thread as I learn more.  
    Sunday, February 19, 2017 3:46 AM
  • Hi,

    Are there any updates?

    You could mark the reply as answer if it is helpful. 

    Best Regards,

    Leo


    Please remember to mark the replies as answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Thursday, March 09, 2017 12:20 PM
    Moderator