[183358] in North American Network Operators' Group
Re: PMTUD for IPv4 Multicast - How?
daemon@ATHENA.MIT.EDU (Valdis.Kletnieks@vt.edu)
Mon Aug 31 12:37:10 2015
X-Original-To: nanog@nanog.org
To: Chris Marget <chris@marget.com>
From: Valdis.Kletnieks@vt.edu
In-Reply-To: <CAAG5dDCZdbYwnoQUuoaxSdevDTAkwyYGtpNfnVWUWWSZzGPMOg@mail.gmail.com>
Date: Mon, 31 Aug 2015 12:37:01 -0400
Cc: "nanog@nanog.org list" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
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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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