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

Question

I've set up my Hyper-V environment (Win 10 Pro 64-bit, update 1809) to have an external virtual switch bound to my wifi adapter and shared with the host OS. I've used this virtual switch with my Debian guest VM to access the internet and the local network.

This was fine up until a couple of days ago when my host's network suddenly dropped network throughput from something like 350Mbps to 8Mbps.

Removing the external switch causes the slowdown to go away completely.

I've tried disabling VMQ, even though my wireless card driver doesn't support it (it's the built-in Qualcomm wifi chip on an Asus Strix z270e motherboard), but that didn't change anything.

Is there a way to have an external switch that shares the connection with the host without these problems, or a resource I can study to figure out how to get around these problems? I need the VM to be exposed to the local network, since I connect to it via test devices connected to my LAN.

Update 1

The answer provided here does describe my situation correctly, and I've tried the solution by making applying the following steps:

1. creating an Internal virtual switch,
2. selecting the internal virtual switch and my wifi NIC in the network control panel and selecting "create bridge" from the context menu.

This resulted in the same slowdown as before with an external virtual switch.

External links

https://win10.guru/hyper-v-external-switches-killing-networking-in-insider-builds

Answer 1

So, I've been fighting this issue myself for a few hours on my nice new laptop, and I believe I've found the combination of settings that seems to have restored most of my connectivity.

Since I have an Intel NIC I have no idea if this will help, but I'm curious and would love for you to try if you haven't gotten it sorted already.

Problem no.1: Slow download Disable coalescing on the Wifi-card. This completely restored my download speed and resolved issues I was seeing with intermittent connectivity in the host OS and on VMs.

Problem no.2: Slow upload Disable Large Send Offload on the Virtual adapter representing the external switch. In my case called vEthernet(WAN)

Answer 2

I have Intel Killer WiFi on an XPS 15 9570 and XPS 17 9700 and Precision 7770 and they have similar issues with Hyper-V. I will give the specific configuration that restored full performance for me:

• vEthernet adapter configured for External access pointing to the WiFi adapter

  • Set “Recv Segment Coalescing (IPv4)” to “Disabled”
  • Set “Recv Segment Coalescing (IPv6)” to “Disabled”
  • Set “Large Send Offload Version 2 (IPv4)” to “Disabled”
  • Set “Large Send Offload Version 2 (IPv6)” to “Disabled”

• WiFi adapter

  • Set “D0 PacketCoalescing” or “Packet Coalescing” to “Enable” (or “Disable”—sometimes changing this setting makes things faster even though one setting used to be better—it doesn’t seem consistent). This setting may not make a difference. Try skipping this step and see if the above vEthernet changes are sufficient first.

Inside of the VM itself, I found I also have to do:

• Ethernet adapter
  • Set “Large Send Offload Version 2 (IPv4)” to “Disabled”
  • Set “Large Send Offload Version 2 (IPv6)” to “Disabled”

Together, these settings restored my host system’s connection speed from 7Mbps to 60Mbps which is the performance I would get if I didn’t have Hyper-V configured at all. I also still get just about the same performance on my guests.

Note that in the latest version of Windows 11, you may need to go to Device Manager to open the hardware properties for your network adapters as it seems to no longer be accessible from Control Panel’s Network and Sharing center.

Answer 3

Disabling Large Send Offload Version 2 in the properties of the external vEthernet adapter helped me with this problem.

Answer 4

I don't know if my suggestion can satisfy what you're really asking but what I've done is instead of using external switches I create an internal one and configure it as a NAT virtual switch..that way I don't have to deal with external vSwitches.. if what you want is to provide internet access to guest VMs it works just fine. Here's a link in case you want to implement it..it's relatively easy. Hope that helps!

Answer 5

Adding another possible cause and solution for Virtual Switch causing very slow download speeds for the entire system (guests and host). This is on Windows 11. The Microsoft NDIS Capture extension was enabled by default. Simply turning this off (unchecking it) restored my normal network performance.

Answer 6

I am just adding the screenshots to make it a little easier.

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

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

Answer 7

I turned off tcp-segmentation-offload in the VM with ethtool -K eth0 tcp-segmentation-offload off. I think you can also use ethtool -K eth0 tso off https://kb.vmware.com/s/article/2055140

Switching this setting off improved my upload and download speed.

Answer 8

My download speed through WiFi is 300Mbps before creating external v-switch. Afterwards, and without any tweaking, speed dropped to single digit. Disabling Packet Coalescing on WiFi adapter increased speed to about 50Mbps. By enabling Throughput Booster, however, speed is fully restored to 300Mbps.

Answer 9

I have a HYPER-V host (Server 2019 1809 & 1903) tested. The Windows 10 guest had fast SMB networking but extremely slow internet browsing/download speeds. My post is NOT related to WiFi may assist anyway.

My Linux guests were getting fast download speeds.

My Windows 10 were setup as Gen2 VM's. I created a Windows 10 VM as Gen1 VM, I'll call this W10G1.

W10G1 still had poor internet performance using 'Network Adapter' in the config. W10G1 had excellent internet performance using a 'Legacy Network Adapter'. No other changes were made.

It appears that there is a problem in the hosts 'Network Adapter' code, or the Windows 10 Guest's 'Network Adapter'.

I'd be happy for someone to double-check my results by doing a similar test.

Answer 10

My scenario of solving this:

• Delete all External cards.
• Create Internal vEthernet card.
• Share internet from my Wi-Fi connection to this internal card.
• Inside Virtual Mashine set lan card to DHCP-auto. This is way you configure NAT and get random IP (192.168.137.45 in my case).
• Port forwarding for my work need.
• In admin console: netsh interface portproxy set v4tov4 listenport=180 connectaddress=192.168.137.45 connectport=80
• This will let your PC listen to 180 and forward it to 80 of VMs. You can set any port forwarding like this.