Very slow up/slow download speeds if Hyper-V external switch enabled

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.

I have found a simple solution for Intel NICs. I have no idea how general this solution is.

OMG - you saved me so much time with this fix tonight. Couldn't figure out why my network performance on download had halved and upload had gone to less than 1Mb from 500Mb. Thank you! I had been building some Linux hosts that I wanted to run as VM's, they all worked great but the alas the host did not :).

Worked for me on the Upload with an Intel Wi-Fi Adapter. Thank you.

For quick ref...

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).

stefantemp said:

For quick ref...

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).

Click to expand...

The main problem is in the "Network virtualisation" - another solution is to attach a separate nic to the VM say a USB device- those modern usb wifi ones are capable of very high speeds.

Host-guest communication is always a pain when NAT is involved -- . Pass thru the actual hardware to the VM usually results in better performance in these cases rather than having to share with the host as in that case tere's then "double" traffic -- first from the target / visited web site via the "virtual nic" on the host and then through the "internal Host / VM" network.

You might get better performance too if you access the VM from a remote machine but RDP is frustratingly slow and not very secure. If it's file transfer you want just use SSH or similar.

Cheers
jimbo

jimbo45 said:

The main problem is in the "Network virtualisation" - another solution is to attach a separate nic to the VM say a USB device- those modern usb wifi ones are capable of very high speeds.

Host-guest communication is always a pain when NAT is involved -- . Pass thru the actual hardware to the VM usually results in better performance in these cases rather than having to share with the host as in that case tere's then "double" traffic -- first from the target / visited web site via the "virtual nic" on the host and then through the "internal Host / VM" network.

You might get better performance too if you access the VM from a remote machine but RDP is frustratingly slow and not very secure. If it's file transfer you want just use SSH or similar.

Cheers
jimbo

Click to expand...

This is a different issue to overall performance.

If Hyper-V is set up to use default network i.e. behind a NAT, Windows works fine in sharing the NIC with Hyper-V.

The issue arises when you are using an external switch so VM and Host are on same subnet (no NAT), then Windows falls over with some NICs (Intel are prone to this), and download/upload speeds are severely reduced. The issue is tied up with large packet sizes which are supposed to improve performance, but does the complete opposite.

There is clearly a bug either in Windows or the drivers, but disabling coalescing usuall sorts it.

cereberus said:

This is a different issue to overall performance.

If Hyper-V is set up to use default network i.e. behind a NAT, Windows works fine in sharing the NIC with Hyper-V.

The issue arises when you are using an external switch so VM and Host are on same subnet (no NAT), then Windows falls over with some NICs (Intel are prone to this), and download/upload speeds are severely reduced. The issue is tied up with large packet sizes which are supposed to improve performance, but does the complete opposite.

There is clearly a bug either in Windows or the drivers, but disabling coalescing usuall sorts it.

Click to expand...

Hi there

I agree - but :

I'm not a Network Guru but it's not hard to tell when you have an internet connection available at nearly 10Gbps and connection between HOST and VM can be as slow as 200mbps/sec even with fast SSD's / Nvme's -- and with spinners it can be much slower - often less than 100mbps.

In my Biased Linux view a Host with KVM/QEMU to a Windows VM I can easily get almost the full USB-C spec between transferring files etc between HOST and VM on Host->VM or VM-> Host communication and on external Internet only limited by the download speed of the target website.

HYPER-V is potentially capable of giving fantastic throughput beteen VM and HOST but a lot of work still seems to be needed on "Virtual NIC vio drivers".

Cheers
jimbo

cereberus said:

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.

I have found a simple solution for Intel NICs. I have no idea how general this solution is.

Very slow up/download speeds with HyperV external switch setup - Windows 10 Help Forums

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 u

www.tenforums.com

Click to expand...

I got a similar problem that, when using bridge network, the upload speed cut down nearly to 0. I then disabled 'large send offload', but when copying file from another machine in LAN, if the speed reach near to 200MB/s, the system crashes immediately.

@cereberus, @Bree, and @johnlgalt

In my case, I could not get it to speed up after putting in the External Virtual Switch in Hyper-V as the host being Windows 11 Beta Insiders is on a Intel AX210 WiFi6E/BT 5.2.

Without the External Virtual Switch added in Hyper-V, my speeds are:
1.410Gbps down/42.06Mbps up (connection is 1.4Gbps down/42Mbps up)

With the External Virtual Switch turned on, it's 310Mbps-389Mbps down/42Mbps up
which is the maximum speed I get before and after the following all done in device manager:
Intel AX210 - disable packet coalescing
disable large send offload (for IPV4 and IPV6) from the external vethernet switch that is bridged which for me is named
Hyper-V Virtual Ethernet Adapter #2 (not the default vethernet switch which is named
Hyper-V Virtual Ethernet Adapter #3).
also tried disable large send offload (for IPV4 and IPV6) on Microsoft Network Adapter Multiplexor Driver as @Bree mentioned on another thread and it makes no difference. I also tried disabling Recv Segment Coalescing (for IPV4 and IPV6) in addition to the previous and it didn't make a difference either.

@Bree, I was looking at your thread and it seems you only have one Hyper-V Virtual Ethernet Adapter in Device Manager, is that with the External Virtual Switch or without it?

Any other ideas on what I can try?

Almighty1 said:

@cereberus, @Bree, and @johnlgalt

In my case, I could not get it to speed up after putting in the External Virtual Switch in Hyper-V as the host being Windows 11 Beta Insiders is on a Intel AX210 WiFi6E/BT 5.2.

Without the External Virtual Switch added in Hyper-V, my speeds are:
1.410Gbps down/42.06Mbps up (connection is 1.4Gbps down/42Mbps up)

With the External Virtual Switch turned on, it's 310Mbps-389Mbps down/42Mbps up
which is the maximum speed I get before and after the following all done in device manager:
Intel AX210 - disable packet coalescing
disable large send offload (for IPV4 and IPV6) from the external vethernet switch that is bridged which for me is named
Hyper-V Virtual Ethernet Adapter #2 (not the default vethernet switch which is named
Hyper-V Virtual Ethernet Adapter #3).
also tried disable large send offload (for IPV4 and IPV6) on Microsoft Network Adapter Multiplexor Driver as @Bree mentioned on another thread and it makes no difference.

@Bree, I was looking at your thread and it seems you only have one Hyper-V Virtual Ethernet Adapter in Device Manager, is that with the External Virtual Switch or without it?

Any other ideas on what I can try?

Click to expand...

Set all Hyper-V vms to default network adaptor.

Remove bridging from network connections.

Remove all hyper-v virtual net adaptors from device manager.

Check wifi speeds are back to normal.

Then either just use default wifi network adaptor in hyper-V.

If you really need an external switch, add one, then go through steps in this post on the newly added hyper-v network adaptor (only one).

cereberus said:

Set all Hyper-V vms to default network adaptor.

Remove bridging from network connections.

Remove all hyper-v virtual net adaptors from device manager.

Check wifi speeds are back to normal.

Then either just use default wifi network adaptor in hyper-V.

If you really need an external switch, add one, then go through steps in this post on the newly added hyper-v network adaptor (only one).

Click to expand...

Thanks!

Yes, I set the only Hyper-V VM I have which is Windows Insiders Canary to the Default Switch.

How do I remove bridging?

In Device Manager, I deleted anything starting with Hyper-V including the hidden devices.

WiFi speeds are back to normal only when the External Virtual Switch is deleted in Hyper-V which removes the Hyper-V Virtual Ethernet Adapter from Device Manager.

I thought the problem with the Default WiFi Network Adapter in Hyper-V was it was extremely slow for the Hyper-V VM while a created switch would be faster, atleast it seemed that way in my post(s) in the thread.

I did add the external switch and went through all the steps for the newly added Hyper-V network adapter, the other way to tell which is which is by looking at the events timestamp of the Hyper-V network adapter and the results are the same as before.

Is a External Switch needed if there were other Windows Machines on the same WiFi LAN to see the Windows 11 Insiders Canary VM for file sharing?