I haven't confirmed the behavior on BSD manually, but based on skimming https://stackoverflow.com/a/14388707/2334407 https://stackoverflow.com/a/14388707/233440

I haven't confirmed the behavior on BSD manually, but based on skimming https://stackoverflow.com/a/14388707/2334407 https://stackoverflow.com/a/14388707/2334407 and https://www.freebsd.org/cgi/man.cgi?query=setsockopt&sektion=2 https://www.freebsd.org/cgi/man.cgi?query=setsockopt&sektion... , I'm inclined to believe their implicit claim that the original behavior of SO_REUSEPORT is to duplicate everything to each listener. In fact, it looks like Linux copied the behavior of SO_REUSEPORT_LB and called it SO_REUSEPORT. Ahhh, the joys of "portability"...