Re: some further musings
Philippe Prindeville <philipp@gipsi.gipsi.fr> Tue, 05 December 1989 17:15 UTC
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Date: Tue, 05 Dec 1989 18:14:53 -0100
From: Philippe Prindeville <philipp@gipsi.gipsi.fr>
Message-Id: <8912051714.AA25461@gipsi.gipsi.fr>
Phone: +33 1 30 60 75 25 / +33 1 47 34 42 74
To: smb@research.att.com
Subject: Re: some further musings
Cc: MTU Discovery <mtudwg>
up. Conforming hosts today shouldn't be sending packets that need fragmentation as long as every hop accepts 576 or larger. This implies that most jumbograms are from hosts that are trying to do MTU discovery, in which case they'd understand the ICMP message. A Except for SUNs with RPC and NFS (but that's hardly any ;-). comparatively small cache could be kept of source-destination pairs that had been sent such messages recently. Since this cache is soft state, it doesn't matter too much if it's lost on a reboot, unless the Ah, the dirty word: state. I don't like building this into IP. We could further embellish this scheme by using the cache when routes change. If the new route to a destination lowers the MTU, flush the cache for that destination -- you want to send new options. If it raises the MTU, flag the cache entries; when any packet flows through for a source-destination pair that's in the cache -- and hence for which the sencder has previously been advised of the proper MTU -- send it a new report to raise the MTU. This last may be overkill, of course... It seems to me that routers are starting to pick up a lot of complex associations here (read: excess baggage). I don't like this. It seems to me that a lot of this "when to" and "when not to" and "what if he won't cooperate" questions (regarding throttle control of Report Fragmentation) messages must have been faced by the Source Quench designers. Perhaps we can draw on their experience? -Philip
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