the problem is, pf/opnsense aren’t based on Linux…
oh, well in that case you should fuck around with BSD someday, i've been meaning to do so, just haven't gotten around to it. the various BSDs are the siblings of linux.
as for all of the networking side of things, networking is just a nightmare, that's just something you have to learn about. Setting up your own local network to figure out how things work in a sterile controlled environment would be good.