From: Mark Andrews <[email-masked]>
Date: Mon, 11 Jul 2011 02:12:19 +1000

References: <[email-masked]> <[email-masked]> <[email-masked]> <[email-masked]> <[email-masked]>  <[email-masked]>
Subject: Re: Spurious MTU in IPv6 RAs Where WAN is PPPoE
In-reply-to: Your message of "Mon, 11 Jul 2011 00:20:03 +0900."
             <[email-masked]>
--------

In message <[email-masked]>, Masataka Ohta writes:
> Iljitsch van Beijnum wrote:
> 
> > But with IPv6 we have a new chance to punish the people creating
> > the problem rather than the ones implementing PMTUD properly,
> > so The Right Thing To Do is NOT fix any PMTUD breakage in
> > properly behaving systems, but rather push people that
> > configure their systems incorrectly to fix this.
> 
> Let's see the reality.
> 
> IPv6 is broken to request packet too big ICMPs must be
> generated even against multicast packets, which causes
> serious periodic ICMP implosions when MTUs are, because of
> tunneling, below 1500 near many receivers and is 1500 at a
> sender and other part of the network.
> 
> It means that rational operators MUST filter some ICMP
> and, not surprisingly, some operators will block all
> ICMP or all packet too big ICMPs, which means PMTUD
> won't work.
> 
> Who are the people to be punished for creating the problem?
> 
> 					Masataka Ohta
> _______________________________________________
> Ietf mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/ietf

Which only happens if applications disable IPV6_USE_MIN_MTU for
multicast packets (the default is to fragment multicast packets
at network MTU (1280)).

So to get this you need a broken stack or a brain dead application.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]