I wonder how well [Wayback/Archive] H3/H2 Net Card – ODROID is supported by pfSense. It is an M.2 based PCIe network card that adds 4 ethernet ports of 2.5 gigabit each to an ODROID H2 or H3 series (so you have 6 ports total), ideal for some hefty router.
Pictures (from the above link) of the board, cases and mainboard below.
But first: Realtek NICs is not vendor supported on FreeBSD (which pfSense and OPNsense are based on).





