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RE: PMTUD and MTU < 1280

"Dan Wing" <dwing@cisco.com> Mon, 25 July 2011 13:36 UTC

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From: Dan Wing <dwing@cisco.com>
To: 'Rémi Després' <remi.despres@free.fr>
References: <264DF4B8-A7F3-4DB3-B58D-BBAC2A48B470@gmail.com> <A3E346FA-E5A4-4755-9D35-08CB10494424@apple.com> <01d201cc48e1$0784d8d0$168e8a70$@com> <010826E2-D6DF-488D-B5C4-CE14E47C7EE7@free.fr>
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Subject: RE: PMTUD and MTU < 1280
Date: Mon, 25 Jul 2011 09:36:23 -0400
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Cc: ipv6@ietf.org, 'RJ Atkinson' <rja.lists@gmail.com>
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> -----Original Message-----
> From: Rémi Després [mailto:remi.despres@free.fr]
> Sent: Monday, July 25, 2011 8:38 AM
> To: Dan Wing
> Cc: 'james woodyatt'; 'RJ Atkinson'; ipv6@ietf.org
> Subject: Re: PMTUD and MTU < 1280
> 
> 
> Le 23 juil. 2011 à 04:34, Dan Wing a écrit :
> 
> >> -----Original Message-----
> >> From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On Behalf
> Of
> >> james woodyatt
> >> Sent: Wednesday, July 20, 2011 2:44 PM
> >> To: RJ Atkinson
> >> Cc: ipv6@ietf.org
> >> Subject: Re: PMTUD and MTU < 1280
> >>
> >> On Jul 20, 2011, at 14:35 , RJ Atkinson wrote:
> >>
> >>> One hopes IPv6 implementers will be tolerant of IPv6 MTUs below
> 1280
> >> bytes, because they do exist in the deployed world and aren't going
> >> away anytime soon.
> >>
> >> Those hopes are not well placed.
> >>
> >> I am aware of at least one packet filter implementation-- which
> might
> >> be refined in the future, one hopes, to conform fully with RFC 6092-
> -
> >> that treats this behavior as a resource exhaustion attack and drops
> >> flows accordingly.
> >
> > Its behavior violates the last paragraph of Section 5 of RFC2460.
> 
> Violation _only in case_ of "an IPv6 packet that is sent to an IPv4
> destination".

But how does one determine an IPv6 packet is, or isn't, going 
to an IPv4 destination?  I don't think it's possible to determine
if there is an IPv6/IPv4 translator on the path.

-d


> If the destination is IPv6, a PMTU below 1280 remains therefore a
> network failure.
> This authorizes a simple IPv6 host to refuse packets beyond 1280 octets
> and to have no support of packet-reassembly.
> 
> Right?
> 
> Regards,
> RD
> 
> 
> 
> >
> > -d
> >
> >>
> >> --
> >> james woodyatt <jhw@apple.com>
> >> member of technical staff, core os networking
> >>
> >>
> >>
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