PMTUD for IPv4 Multicast - How?

Valdis.Kletnieks at vt.edu Valdis.Kletnieks at vt.edu
Mon Aug 31 16:37:01 UTC 2015


On Mon, 31 Aug 2015 12:12:16 -0400, Chris Marget said:

> 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".

Don't send multicast packets with DF set.
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