Slow download speed after creating External Virtual Switch

I have the exact same problem.
Any help would be appreciated.

As of 1709 a Default Switch is created so you may not need an external switch.

Details about the Default Switch

The switch named “Default Switch” or “Layered_ICS”, allows virtual machines to share the host’s network connection. Without getting too deep into networking (saving that for a different post), this switch has a few unique attributes compared to other Hyper-V switches:

• Virtual machines connected to it will have access to the host’s network whether you’re connected to WIFI, a dock, or Ethernet.
• It’s available as soon as you enable Hyper-V – you won’t lose internet setting it up.
• You can’t delete it.
• It has the same name and device ID (GUID c08cb7b8-9b3c-408e-8e30-5e16a3aeb444) on all Windows 10 hosts so virtual machines on recent builds can assume the same switch is present on all Windows 10 Hyper-V host.

Hyper-V virtual machine gallery and networking improvements | Virtualization Blog

You could try that instead (upgrade from 1703 to 1709 and delete external switch) - I don't see this issue on 1709 but then my connection is perhaps too slow (100 Mbps up/down).

cereberus said:

Have you set the number of cores to 8 in hyer-v settings (virtual processor). No idea otherwise.

Hello cereberus.
I was not clear in my first post. The slow download speed is not a problem of a virtualized OS, but the Windows original installation. The speed drops as soon as I enable the External Virtual Switch.

lx07 said:

As of 1709 a Default Switch is created so you may not need an external switch.
Hyper-V virtual machine gallery and networking improvements | Virtualization Blog
You could try that instead (upgrade from 1703 to 1709 and delete external switch) - I don't see this issue on 1709 but then my connection is perhaps too slow (100 Mbps up/down).

Hello lx07, I already have the 1709, but form what I've read so far, the thing with the Default switch is it used NAT, and I want my VM's to have access to my internal network.

Regards.

Portugal said:

I already have the 1709, but form what I've read so far, the thing with the Default switch is it used NAT, and I want my VM's to have access to my internal network.

That is true.

There are a couple of suggestions here if you didn't see it already - either disable VMQ on the NIC or make sure RSS Base processor number is set to 0.

server 2012 hyper-v vSwitch performance is terrible

lx07 said:

That is true.

There are a couple of suggestions here if you didn't see it already - either disable VMQ on the NIC or make sure RSS Base processor number is set to 0.

server 2012 hyper-v vSwitch performance is terrible

Hello lx07, my NIC does not support VMQ, even using powershell :-(

Regards.

I had the same problem and updating my network adapter drivers (in Device Manager) fixed my problem.

I just installed Windows 10 Pro on a Dell M6800 in Dec 2017, so I thought that all of my drivers were up to date, apparently they were not.

Portugal said:

When the External Virtual Switch is enabled, I assume the download speed is lower due to the fact one CPU core is being maxed out, my question is why? Why isn't the load spread throughout the cores?
Is anyone experiencing a similar issue?

I had a similar issue (I was not so thorough as to check all the resource usage graphs though!). In my case, the Hyper-V host (Win 10 Pro) experienced slow networking on downloads only (uploads were just fine), after creating an External Hyper-V virtual switch. Trashing the Hyper-V switch reliably restored download performance.

My physical adapter is an 'Intel(R) Ethernet Connection (2) I219-V #2'.

At my wit's end, chasing down driver updates, fussing with RSS paramters (clearly, it was a 'receive side' problem), stressing over absent 'VMQ' attributes allegedly present on some adapters (but not mine) as directed in mindless ways by people on the internet who don't know how to read ....
... I finally wondered if one of the protocols bound to the Hyper-V switch was interfering with it. Recall, that when Hyper-V sets up an external switch, it automatically (and blindly) migrates almost all the protocols bound to that NIC, to the new virtual NIC.

Spotting 'Intel(R) Technology Access Filter Driver' enabled, I reasoned that it may not apply to a Hyper-V virtual NIC, and turned it off.
Success! Full download speed returned!