Hiya, tomk!

Sorry in advance I'm not much help. In a terminal, do `man ifconfig` and `man nfe` to read the manpages for ifconfig and the nfe driver. You can use ifconfig(8) then to set a media option and force full-duplex ... dunno if it will help/make a difference.

As for a driver problem, the nfe(4) driver is the correct driver for the nForce 51. What version of FBSD are you running? It could well be, if it's an older one, that updating would help ... because you'd likely get corrected driver code (if it is indeed a driver issue).

Best of luck!