Hyper-V Dropping Outgoing Packets

For weeks I have been fighting with a Windows Server 2008 R2 server running Hyper-V. I noticed that on a couple of virtual machines they would suffer from significant packet loss. I first noticed it with the Windows 8 Release Preview VM and immediately blamed it on Windows 8 not being supported yet, not being released yet, etc. But, then I noticed the same thing on a Windows Server 2008 R2 VM. After some trial and error I was able to determine that the serious packet loss was in outgoing packets, say for example, copying a large (1 GB) file from the VM to network share (hosted on another physical computer). The really troublesome thing was that the packet loss was not just in the VM, but the host server would drop packets too! This was significant packet loss – so significant that I could not maintain a Remote Desktop RDP session to the Hyper-V server. Running a ping would show that packet loss would go on for minutes before a response was returned. And when it was returned, I was lucky to get more than one before long periods of loss again. I scoured the internet and found lots of people with the same or similar problem – and many with solutions – none of which worked for me.

I tried updating the host network drivers, making sure to install/update the manufacturers drives (as opposed to Windows drivers). I tried updating the host BIOS. I tried installing various hotfixes (including 2263829 & 974909). I tried this list of recommended hotfixes for Hyper-V. I tried deleting and recreating the network connections, both on guest AND on host. I tried using a different hardware switch. I tried different hardware NIC. I tried moving the VMs to a different physical disk. Nothing worked. Until…

I nearly gave up. I had no idea why only a couple VMs had an issue and others did not. Then I decided that since the problem was only with outgoing packets, I would try changing the properties on the guest NIC. As soon as I disabled the Large Send Offload Version 2 (IPV4) and Large Send Offload Version 2 (IPV6) config values on the Microsoft Hyper-V Network Adapter Advanced Properties, things started working like a charm!

Hyper-V Network Adapter LargeSendOffloadIPV4 Hyper-V Network Adapter LargeSendOffloadIPV6

I still don’t know why this was necessary on only a couple VMs and not others. I just know servers and networks are once again reliable.


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10 Responses to “Hyper-V Dropping Outgoing Packets”

  1. I have been looking for this document for some time. I’m experiencing the exact same problem and large packet offload was set on both IPv4 and IPv6, if this fixes my problems, you will be my hero :)

  2. Dot says:

    Thanks! I have been noticing the exact same issue with Windows 8 VM on Server 2008 R2. Disabling the large send offload setting worked for me too! I wonder if the issue has something to do with how Windows 8 handles networking traffic through a virtual adapter on an older windows/hyper-v platform.

  3. Brandon says:

    Thank you so much! This fixed the problem on my Windows 7 32-Bit Hyper-V VM.

  4. Nick says:

    Perfect! Been working on this all morning.

    I was in a bit of a pickle as I checked out a huge project on through TFS, worked on it, tried to check it back in aaaaand… VM’s network crashed and TFS cut me off.

    Now I’ve turned those Large Send Offloads off, it works as expected.

    My environment was:
    Host machine: Windows 8.1 running Hyper-V 6.3.9600.16384
    Virtual machine: Windows Server 2008 R2 SP1

    Perfect inbound network activity
    Gimped outbound network activity
    (This can be confirmed using a broadband speed test website on both host and vm)

    Note that only the network adapter on the VM needed to be altered, not on the host machine.

  5. Mangus says:

    Great work! Just did it and been working for 10 minutes, I was getting dropped from RDP session to my VM almost every time I clicked my mouse!

    My environment is:
    Host machine: Windows Server 2012 Standard
    Virtual machine: Windows 8.1 Enterprise

    Note, unlike Nick above, I only altered the host machine network adapter and its working great!

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  7. Lola says:

    Thanks for this!

  8. Keith Seda says:

    This did not fix my problem. I ended up having to use a different NIC, the different NIC stopped the connection issues and dropping packets.

  9. Jesse P says:

    host: Windows 10 Enterprise
    guest: CentOS 7 Linux

    Was dropping outbound ping packets in big chunks, next to useless- but inbound pings were fine like you said. But I didn’t change the guest’s network settings, I changed the host’s “Hyper-V Virtual Ethernet Adapter” which is the adapter it creates when you make a new Virtual Switch in Hyper-V’s manager. Disabled the Large Send Offload stuff like you said. All good after that. Thank you so much!!!!

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