Network speed in FreeBSD on Hyper-V

Very often experts of Unux/Linux systems and Windows systems argue among themselves which is better. And I remember the phrase - "You don't like cats? Yes, you just do not know how to cook them.«
And the thing is that in fact the truth is somewhere in between. Both systems are good in their own way, and it is important to apply these systems where they are most effective. But there is another nuance, thisKnow how to set up correctly» And in this article, we will touch on one small problem that manifests itself if you have a Windows-based hypervisor and a Hyper-V virtualization environment, and a FreeBSD virtual machine. In this configuration, the network speed in FreeBSD on Hyper-V will be slow.

The cause of this problem is the FreeBSD 12.3 and 13 kernel. These versions do not support Receive Segment Coalescing (RSC) technology.


1. Check if RSC is enabled for virtual switches. To do this, enter the following command in PowerShell:

Get VMSwitch | % { $_ | Select-Object *RSC* }

2. Disable software RSC:

Set-VMSwitch -NameVirtualSwitchName> -EnableSoftwareRsc $false

- must be replaced with the name of your virtual switch.

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