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Re: Evolution of the IP model - ICMP and MTUs

Templin, Fred L  - Le 8/18/08 4:30 PM :

-----Original Message-----
From: Rémi Després [mailto:remi.despres@free.fr] Sent: Sunday, August 17, 2008 11:46 PM 
To: 'Dave Thaler'; Dan Wing
Cc: 'v6ops'
Subject: Re: Evolution of the IP model - ICMP and MTUs


1.
Thanks Dan for the ref. to RFC 4963. I had not noticed this RFC, important as far as the evolution of the IPv4 model is concerned.
IMU, since it shows that, at high data rates, IPv4 fragmentation can lead to undetected data corruption at the IP layer, it implies that fragmentation SHOULD be discarded from an updated IPv4 service model (the DF bit MUST be set in all packets). 

IMHO, this is taking too narrow a view. The case to be
avoided is *sustained* fragmentation at high data rates.
A little bit of fragmentation is OK as long as it can be
detected and tuned out asap. In some instances, that may
mean setting DF=0.


Yes, you are right.
(As a matter of fact, I had first written that it implied "in practice". It would have been better kept that way).
I have doubts however that the logic to manage that "little bit of fargmentation" would be worth it.
Taking the risk that corrupted data would be received, if this logic happens to be ill tuned when data rates have continued to increase, should IMHO not be recommended. 

Recommending a simple and robust logic would be preferable.

RD