In a message written on Wed, Aug 20, 2008 at 09:43:44PM +0530, Glen Kent wrote:
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. -- Leo Bicknell - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/