My boss at an internship bought like 20 NE2000 NICs for cheap somewhere in the late 1990's. We were confused when we would plug a second one in and it all went

My boss at an internship bought like 20 NE2000 NICs for cheap somewhere in the late 1990's. We were confused when we would plug a second one in and it all went to heck no matter which 2 NICs we used. We realized they all had the same MAC address. So we just overrode the MAC in the OS and got them to work. Someone cloned a card perfectly :)