On Wed, Aug 12, 2020 at 10:29:56PM -0700, Jay Vosburgh wrote: > Did you notice this by inspection, or did it come up in use > somewhere? I can't recall ever hearing of anyone using broadcast mode, > so I'm curious if there is a use for it, but this change seems > reasonable enough regardless.
I did actually encountered our customers using broadcast mode twice. But I have to disappoint you, their "use for it" was rather an abuse. One of them had a number of hosts, each having two NICs in broadcast mode bond, one connected to one switch and one connected to another switch (with no direct connection between the switches). Having each packet duplicated when everything worked triggered some corner cases in networking stack (IIRC one issue in fragment reassembly and one in TCP lockless listener). Thankfully I was eventually able to convince them that this kind of redundancy does not really work if one host loses connection to one switch and another host to the other. I don't remember the other use case from the top of my head but I'm quite sure it made even less sense. Michal