Subject: [v6ops] Minimum MTU size

From: Dragos Ilie <[email-masked]>
Date: Tue, 31 Jan 2012 10:50:25 +0100

Hello!

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.

My apologies if this is the wrong forum for asking this question.

Sincerely,
Dragos

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From: Francis Dupont <[email-masked]>
Date: Tue, 31 Jan 2012 11:17:59 +0100

>  for the 1280-byte choice in the case of IPv6 or point me to relevant

=> 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

[email-masked]

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From: Dragos Ilie <[email-masked]>
Date: Tue, 31 Jan 2012 11:40:39 +0100

Thank you! That is what I was looking for.

Regards,
Dragos Ilie

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From: Brian E Carpenter <[email-masked]>
Date: Wed, 01 Feb 2012 08:55:01 +1300

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:
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