[107028] in North American Network Operators' Group
Re: IP Fragmentation
daemon@ATHENA.MIT.EDU (Leo Bicknell)
Wed Aug 20 13:24:49 2008
Date: Wed, 20 Aug 2008 13:24:40 -0400
From: Leo Bicknell <bicknell@ufp.org>
To: OPS Gurus <nanog@merit.edu>
Mail-Followup-To: OPS Gurus <nanog@merit.edu>
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In a message written on Wed, Aug 20, 2008 at 09:43:44PM +0530, Glen Kent wr=
ote:
> Do transit routers in the wild actually get to do IP fragmentation
> these days? I was wondering if routers actually do it or not, because
> the source usually discovers the path MTU and sends its data with the
> least supported MTU. Is this true?
Yes.
A GigE jumbo frames host (9120) to a standard POS interface (4420)
to a DS3 customer (1500) happens, and the GigE->POS and POS->DS3
routers must both do fragmentation.
> I would wager that the vendors and operators would want to avoid IP
> fragmentation since thats usually done in SW (unless you've got a very
> powerful ASIC or your box is NP based).
As far as I know the "big" routers all do it in hardware with no real
performance penality; but I haven't studied in detail.
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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