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I have a 100 Mbps fiber connection I'm connecting to over WiFi (ASUS PCE-AX58BT AX3000 Dual Band - Intel Wi-Fi 6 AX200 160MHz), though note that the routers do not support WiFi 6 (NETGEAR R6200v2 -> ZTE F660). Recently, after creating a Hyper-V Virtual Switch on Windows 10, I started experiencing slow upload speeds, but not download. After a lot of experimentation and research, I figured out that disabling Large Send Offload v2 IPv4 would seem to fix the problem. Additionally, deleting the Network Bridge, thereby converting the External Virtual Switch to Internal also seemed to fix the Upload speed issue.

I would like an explanation on the situation.

  1. Why only with the Virtual Switch/Bridge
  2. How does the workaround work?
  3. Why upload and not download (The research I did online seemed to suggest this issue also impacted download, but maybe it was when communicating between local Windows machines)?
  4. Does this issue impact only certain hardware, as a certain laptop didn't exhibit this issue.

What I suspect is that when Bridged, windows erroneously tries to use offload on hardware that does not support it, but I'm not sure.

harrymc
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dVVIIb
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  • Does this answer your question? [Hyper-V External network switch kills my host's network performance](https://superuser.com/questions/1266248/hyper-v-external-network-switch-kills-my-hosts-network-performance) – harrymc May 16 '21 at 20:32
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    @harrymc, Thanks, but disabling LSOv2 does seem to do the trick for me. I just want to know why/how it works, an explanation. – dVVIIb May 17 '21 at 08:22

1 Answers1

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I had a similar network performance issue on the laptops, but it only affected the ethernet upload speed. After disabling LSO, I was able to achieve a full symmetrical gig over the wired network.

Bitdefender suggests disabling LSO to improve performance and gives a brief explanation: https://www.bitdefender.com/support/Large-Send-Offload-causes-performance-and-slowdown-issues-459.html

Others suggest LSO does not work very well and points to NDIS implementation: https://learn.microsoft.com/en-us/windows-hardware/drivers/network/offloading-the-segmentation-of-large-tcp-packets

winstein8532
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    As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Jan 15 '23 at 16:40