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2011-07-10 11:13:31





References: 
<357D4DFB-95CF-43B3-AABD-7C237AC7B6D7(_at_)sabahattin-gucukoglu(_dot_)com> 
<CEE67A11-B91B-4BAD-B75F-19AFC25CFDFE(_at_)apple(_dot_)com> 
<48BBAE96-4557-436F-A8CC-699BA1E163CF(_at_)sabahattin-gucukoglu(_dot_)com> 
<C4293C11-766E-4E8E-9B77-2F9C5E19BC88(_at_)sabahattin-gucukoglu(_dot_)com> 
<7E362046-C8D4-4160-9865-ABFB1B3C767C(_at_)muada(_dot_)com>  
<4E19C323(_dot_)7020405(_at_)necom830(_dot_)hpcl(_dot_)titech(_dot_)ac(_dot_)jp>
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."
             
<4E19C323(_dot_)7020405(_at_)necom830(_dot_)hpcl(_dot_)titech(_dot_)ac(_dot_)jp>
--------

In message 
<4E19C323(_dot_)7020405(_at_)necom830(_dot_)hpcl(_dot_)titech(_dot_)ac(_dot_)jp>,
 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
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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: marka(_at_)isc(_dot_)org
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