Do you know if I have to do that with regular FreeBSD as well? Like if I were to run just FreeBSD and not pfSense.

The answer here is 'Yes'. TSO and routing / packet filtering are incompatible.

https://wiki.freebsd.org/10gFreeBSD/Router#Disabling_LRO_and...

So why isn't it disabled out of the box (on pfSense, not FreeBSD)?

They are.

https://doc.pfsense.org/index.php/Tuning_and_Troubleshooting...

Do you know when this was instituted? I'm quite sure that wasn't the default when I set up my pfSense systems..

I don't on my FreeBSD hosts and haven't had any problems, but I think it depends on the drivers you have installed. On all my production servers I use standalone Intel NICs w/ the Intel drives; pfSense may be using something else depending on the configuration. FWIW, pfSense has been basically stock FreeBSD + software/skin for the past couple of years.

> FWIW, pfSense has been basically stock FreeBSD + software/skin for the past couple of years.

While we try to move things upstream as much as possible, there are still patches in pfSense that don't make sense for FreeBSD.

> I don't on my FreeBSD hosts and haven't had any problems

TSO and routing/forwarding (and thus filtering) are incompatible.

yep, use Intel e1000e NICs for freeBSD on VMware hosts.

FWIW, I have seen that advice given for problems with networking performance in virtualized environments, regardless of the operating system.