Re: [UPDATE] zerocopy.. While working on ip.h stuff

From: Michael Peddemors (
Date: Mon Feb 26 2001 - 20:53:30 EST

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.

"Catch the magic of Linux...."
Michael Peddemors - Senior Consultant
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