OPNsense Throttling Download Speed on Virtualized Setup (XCP-NG)

[Lorenzo Bot]

Good morning, community.

I'm currently facing a problem that I haven't been able to solve and would really appreciate your help or insights.

I recently deployed OPNsense in my network setup and have been experiencing some performance issues. The firewall is running as a virtual machine on an XCP-NG hypervisor. I followed all the recommended steps from both the OPNsense and XCP-NG documentation. Specifically:

I installed the guest tools (os-xen).
I disabled checksum offloading both in OPNsense and on the virtual NIC in XCP-NG.

Despite these configurations, I'm still having trouble. My internet connection is 1 Gbps down and 500 Mbps up, and it works fine when connected directly. However, once traffic is routed through the OPNsense VM, the download speed drops significantly to around 300 Mbps, while upload remains stable at 500 Mbps.

Interestingly, during a speed test, the OPNsense web interface and graphs become very sluggish or even freeze when the download portion of the test is running. During the upload portion, everything behaves normally without any lag.

Has anyone experienced similar behavior or does anyone have any suggestions on how to troubleshoot or resolve this?

Thanks in advance!