RE: Evolution of the IP model - ICMP and MTUs

["Templin, Fred L" <Fred.L.Templin@boeing.com>]

>-----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.

Fred
fred.l.templin@boeing.com

>Applications that can send datagrams longer than typical MTUs (AFAIK, 
>Sun NFS needs 8 K) can still work in strict conformity with the IP 
>model, but in IPv6.
>
>2.
>With no fragmentation in the IPv4 model, packet losses due to
>insufficient reassembly resources are no longer a concern.
>
>3.
>Where ICMP is not filtered by FWs, upper layers can take advantage of
>MTU information which, since RFC 1191 of 1990, may be returned 
>in Packet 
>too Big ICMP massages.
>
>Rémi Després
>
>
>