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Re: Genart telechat review of draft-ietf-6man-rfc1981bis-06

Stewart Bryant <stewart.bryant@gmail.com> Wed, 26 April 2017 08:48 UTC

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Subject: Re: Genart telechat review of draft-ietf-6man-rfc1981bis-06
To: Joe Touch <touch@isi.edu>, gen-art@ietf.org
References: <149305392811.25808.15115824976388262628@ietfa.amsl.com> <497d3868-406a-a38f-56d8-391b0fc16032@isi.edu>
Cc: ipv6@ietf.org, ietf@ietf.org, draft-ietf-6man-rfc1981bis.all@ietf.org
From: Stewart Bryant <stewart.bryant@gmail.com>
Message-ID: <a974da1d-a9e7-8c64-8086-0955f2dffb12@gmail.com>
Date: Wed, 26 Apr 2017 09:48:43 +0100
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On 25/04/2017 19:26, Joe Touch wrote:
> Hi, Stewart,
>
>
> On 4/24/2017 10:12 AM, Stewart Bryant wrote:
>> Minor issues:
>>
>>   A node MUST NOT reduce its estimate of the Path MTU below the IPv6
>>   minimum link MTU.
>>
>> SB> I missed this last time.
>> SB>
>> SB> Presumably you mean "A node MUST NOT reduce its estimate of the
>> SB> Path MTU below the IPv6 minimum link MTU in response to such
>> SB> a message."
> This seems fine to me, FWIW - i.e., limiting the advice in this doc to
> the mechanism in  this doc.
>
>> SB>
>> SB> Otherwise I would have thought that this was entirely a matter
>> SB> for the host whether it wanted to use a Path MTU below the IPv6
>> SB> link minimum. Nothing breaks if the host takes a more conservative
>> SB> decision.
> I don't agree; the host at that point is violating RFC2460. It should
> never think that an IPv6 link or path with an MTU below what RFC2460
> requires is valid.
>
> Joe
>

That is as maybe, but a host can do more or less what it wants, so this 
is surely an
unenforceable constraint, or are you telling me that the receiving host 
MUST drop a
fragment that is shorter than this? In which case the question whether 
in practice
they do, and whether such a constraint is reasonable.

- Stewart

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