PfSense 2.6.0: Slow network connection on Hyper-V - What can I do?

by Tuto Maker - Published 22/12/2022 - Updated 06/09/2024

What's in the box?

If, like me, you're using the Hyper-V hypervisor and you're trying to install a PfSense VM in version 2.6.0, then you've probably noticed that the PfSense 2.6.0 network connection is slow on the VM. So much so that you're looking for a solution....! The good news is that the solution exists!

1. Hyper-V and PfSense 2.6.0: the problem found

When using PfSense 2.5.2 or an older version on Hyper-Vthis is done correctly. No matter what version of Windows Server you have. However, as soon as you upgrade to the latest version, PfSense 2.6.0, things start to go wrong...!

The network is particularly slow on both the LAN and WAN cards of the PfSense firewall, for cards connected to the physical network as well as those belonging to a virtual network. If you prefer, upload and download speeds are very low and/or capped.

Even if there may be differences in behavior between versions of Windows Server (used to host the PfSense VM), the problem is there. This applies at least to Windows Server 2016, Windows Server 2019 and Windows Server 2022.

What I've found is that this problem isn't related to a bad network card driver or a hardware performance issue per se. It's really a problem between PfSense 2.6.0 and Hyper-V.

2. PfSense network slowness: the solution

To solve this problem, we're going to apply a solution discussed on the Netgate forum (official PfSense). It turns out that a PowerShell command needs to be run as administrator. Here's the command:

Set-VMSwitch -Name "Nom-vSwitch" -EnableSoftwareRsc $false

You might ask: what's this command? The command Set-VMSwitch is used to configure a Hyper-V virtual switch using PowerShell. As for the " -EnableSoftwareRsc" is used to deactivate the RSC function (Receive Segment Coalescing) in the vSwitch. In fact, RSC is a function that reduces the CPU usage of the physical host by merging several TCP segments in order to optimize flows. Clearly, not everyone is happy about this...!

You need to run this command several times: on each vSwitch used by your PfSense firewall. The result is immediate.

This is an example of a PfSense virtual machine, but if you're experiencing network slowness with another virtual machine, you can try out this tip too!