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Re: [v6ops] Minimum MTU size

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 31 January 2012 19:55 UTC

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Date: Wed, 01 Feb 2012 08:55:01 +1300
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Dragos Ilie <dragos.ilie@gmail.com>
References: <CAOLNa-fXX9+qY8Sw-r9WTq6y7wSxNS-XZCfrGXZHmA731x1i9Q@mail.gmail.com> <201201311017.q0VAHxWd053879@givry.fdupont.fr> <CAOLNa-cTBwriS4LBP3KAVUdoM9m_B1HPV8zJ-S9-j6MOBfBkBQ@mail.gmail.com>
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Cc: v6ops@ietf.org
Subject: Re: [v6ops] Minimum MTU size
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I think it was noted at the time that this allowed easily for some
tunnel header overhead within a 1500 link MTU packet, and was therefore
a reasonably efficient value.

BTW 576 = 512 + 64, and I'm sure that isn't a coincidence either.

Regards
   Brian Carpenter

On 2012-01-31 23:40, Dragos Ilie wrote:
> Thank you! That is what I was looking for.
> 
> Regards,
> Dragos Ilie
> 
> 
>
> On Tue, Jan 31, 2012 at 11:17 AM, Francis Dupont
> <Francis.Dupont@fdupont.fr> wrote:
>>  In your previous mail you wrote:
>>
>>>  I am trying to find out the underlaying reason to select a 1280 bytes
>>>  minimum MTU for IPv6 (as opposed to any other value such as 1400 or
>>>  1500 bytes). For example, I heard that the reason for selecting a
>>>  576-bytes min MTU for IPv4 has to do with packet sizes for DNS and
>>>  X.25. I would appreciated it if somebody can explain the motivation
>>>  for the 1280-byte choice in the case of IPv6 or point me to relevant
>>>  information sources.
>> => first the min MTU for IPv4 is 68 bytes (maximum sized header + 8),
>> not 576 which is the minimum size for the reassembly (1500 for IPv6).
>> The choice of 1280 was for 1024 of data (aka application payload) and
>> 256 for headers.
>>
>> Regards
>>
>> Francis.Dupont@fdupont.fr
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