have a machine with 2 network adapters. One connected inside your network, and one outside.
is there something to get a raspberry pi to have two ethernet ports? i would like to avoid buying an optiplex just to use as a gateway, especially if it will be running at all times. worst case, i *could* make it the file server as well, since i also still need a machine that takes 3.5” drives that isn’t some big PC. that way i won’t have to get two optiplexes.