BCE on FreeBSD and oversized packet acceptance.

[Kevin Oberman]

> Date: Sat, 15 Sep 2007 06:55:17 -1000
> From: Randy Bush <randy at psg.com>
> Sender: owner-freebsd-net at freebsd.org
> 
> > what size is the actual maximal sized jumbo packet we will ever see?
> 
> some transpac science community folk, who care more about speed trials
> with big data sets than they do about over-stretching the ethernet crc,
> use 9k jumbo frames.

Almost the entire global R&E community uses 9K frames. This includes
Internet2 (USA), Geant (Europe), Red Clara (S. America), CA*net (Canada),
CUDI (Mexico), AMPATH (S. America), Transpac, Kreonet (Korea), NASA
(USA), and ESnet (USA).

9000 (just to clarify the meaning of 'K') is the MTU recommended by
the Joint Engineering Taskforce, a group which is a consortium of US and
Canadian R&E networks and adopted almost universally in the global
community. This will allow for multiple stacked VLAN and/or MPLS tags on
an 8K byte data packet.

Note that most systems use an 8192 byte IP MTU as that usually affords
better performance as the data portion of the packet will fit in a
single page of memory on most systems.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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