Very slow up/download speeds with HyperV external switch setup

A long standing issue for many Hyper-V users is when you set up an external wifi switch in Hyper-V, it kills the download and/or upload speeds.

On my ASUS with an Intel NIC, my uploads and downloads are only 2% of normal speeds making internet virtually useless.

The problem does not arise with the default switch but that is behind a NAT which makes it very difficult to RDP direct to VM.

I have found a solution that works for me, and I am now back at full speed.

Slow download - disable packet coalescing on the wifi card settings in device manager.

Slow upload - disable large send offload (for IPV4 and IPV6) from the external vethernet switch that is bridged (not the default vethernet switch).

I have no idea if this works for other network adaptors but seems to work for Intel NICs.

Source of information (credit to Mike in post #6).

virtualization - Creating an external virtual switch on Hyper-V causes host to experience very slow networking - Super User


Edit 1: After a bit of testing, it seems you can reenable packet coalescing again after you have disabled it. I suspect there is an initialisation file that gets updated correctly first time you disable it, and then it works fine after that. Obviously disable it again, if downloads are affected.

I also tried reenabling the large send offloads, and the upload speed died again. So for time being, they should remain disabled.

Edit 2: I went back to my old laptop to see if I could fix the same issue with a Qualcomm Atheros QCA61x4 wifi card. I tried lots on combos on web but none worked. So I looked at the network driver, and the hyper-v "external" virtual adapter and found five settings referring to "coalescing" in setting name and disabled them all.

My flabber was gasted - it worked! I have full internet speed with the external switch enabled - I can now RDP to Hyper-V vms directly.

I have no idea which particular setting(s) fixed it but on grounds, "if it ain't broke (anymore), don't fix it", I have no intention of trying to work out which one or more did the trick.

So, if you have similar issues, try disabling anything with coalescing in setting name.

It's taken me over four years to solve this, but then my colleagues at work say I am a persistent b%%%%%rd when trying to solve a tricky problem - LOL!!!

Starlet7222 said:

Thank you so much for this. When I disabled this setting on the Host, my full upload speed returned. Then inside the guest VM, I also had to disable these same settings to get my upload speed bacvk in there too

Oh that is interesting re. vm. I never looked at that before.