I believe we have come accross a bug in Windows Server 2019 Hyper-V.
Does anyone in here know how to report this to Microsoft?
To make some virtual network appliances work, we need to activate the function "Mac Address Spoofing" on the vNIC of the VM's internal interface.
This is needed for VPLS setup and for a VPN concentrator setup.
The function is working, but with highly reduced performance, especially upload goes from 800 Mbit/s to 30 Mbit/s, and ping latency from 1-2 ms to 5-8 ms.
We have tried Mikrotik routers, pfSense, SoftEther on Windows, and we even set up a Windows Server as a router, and the issue is present i all cases.
It only appears then the VM acts as a router, that is traffic coming in through one interface and out through another, and only when Mac Address Spoofing is activated.
We have tried similar setup on VMware where the similar setup requires something called "promiscuous mode", and it works fne with the same VM's.
To make the test complete, we also tested with a Server 2016 Hyper-V, and that works as well.
So Mac Address Spoofing Works in Windows server Hyper-V 2016, but not in Windows server Hyper-V 2019.
Best regards, Ulrich - novaram