> > > At first, I thought this was a bug, but then learned that RFCs 1112, 1122 > > > and 1812 all specify that ICMP unreachables not be sent in response to > > > multicast packets. > > > > > I'm struggling to grok the rationale behind not sending unreachables in > > > response to multicast packets. It seems to me that our networks put IPv4 > > > multicast speakers in a position where it's impossible for them to do the > > > right thing. > > > > For the exact same reason that replying to an ICMP Echo Request sent to > > your broadcast address is generally considered a Bad Idea. > > > > The obvious solution is "Doctor, it hurts when I do that" "Don't do that > > anymore". > > > > It's not as obvious to me as it is to you. I mean, v6 *requires* exactly > this behavior, so it can't be all that bad, can it?
ICMP replies to multicast packets can cause ICMP "implosion". This is not a new discussion - see for instance http://mailman.nanog.org/pipermail/nanog/2012-June/048685.html Steinar Haug, Nethelp consulting, sth...@nethelp.no