From: Michael Peddemors <michael@linuxmagic.com>
Reply-To: michael@linuxmagic.com
Organization: Wizard Internet Services
To: Craig Milo Rogers <rogers@ISI.EDU>
Subject: Re: [UPDATE] zerocopy.. While working on ip.h stuff
Date: Mon, 26 Feb 2001 17:53:30 -0800
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In-Reply-To: <2137.983232656@ISI.EDU>
Cc: linux-kernel@vger.kernel.org
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On Mon, 26 Feb 2001, Craig Milo Rogers wrote:

> > > I have a whole 40 bytes (+/-) to share...  Now although I don't see
> > > anything explicitly prohibiting the use of unused IP Header option 
..
> > > in between.. Has anyone seen any RFC that explicitly says I MUST NOT?
> >
> >Not to my knowledge.  Routers already change the time to live field,
> >so I see no reason why they can't do smart things with special IP
> >options either (besides efficiency concerns :-).

I know they 'rewrite/extend' existing options, but have never seen a case 
where a router adds an option to a packet beyond those based on what the 
original sender set..

> I've forgotten how the Stream ID option was implemented, but I
> won't be surprised if a router inserted it on the fly (but it was
> probably inserted by end systems).  On the other hand, there was also

Hmm, have to look at a little history..

> a competing philosophy that said that the IP checksum must be
> recomputed incrementally at routers to catch hardware problems in the
> routers, and an incremental recomputation when changing the size of
> the header would be more work.

ah.. we do recalculate IP Checksums now..  when we update any of the 
timestamp rr options etc..

> The one thing I would worry about is unleashing mutant IP
> packets upon the world at large.  I hope the proposed experiments have
> a very good firewall.  It would be very nice to attempt to acquire an
> officially blessed IP option number for such experiments before
> unleashing these packets upon an unprepared world.
>
> 					Craig Milo Rogers

Ah, we better have a good firewall <wink> No, if this goes past concept 
phase, we will try for de official bless.


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