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Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04

Joe Touch <touch@isi.edu> Wed, 15 February 2017 21:12 UTC

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To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Stewart Bryant <stewart.bryant@gmail.com>, Stewart Bryant <stewart@g3ysx.org.uk>, gen-art@ietf.org
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From: Joe Touch <touch@isi.edu>
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Cc: ipv6@ietf.org, ietf@ietf.org, draft-ietf-6man-rfc1981bis.all@ietf.org
Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
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Brian (et al.),


On 2/10/2017 11:45 AM, Brian E Carpenter wrote:
>> practice the
>> Internet breaks the mechanism. However it breaks it is a way that seems
>> disruptive to some user traffic. The document is really guidance
>> one how hosts might use  ICMP for optimization, and arguable need
>> not be a standard at all.
> I think that's a mischaracterisation of the mechanism (and the draft).
> PMTUD is not an optimisation. Without it, you get black holes
PMTUD is an optimization to avoid fragmentation.

Without it, you use fragmentation (which has overheads and other
consequences, notably for IPv4).

However, it is only *with* PMTUD (and ICMP blocking) that you get black
holes.

Joe

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