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Date: Tue, 09 Feb 2010 20:22:59 +0800
From: Ilya Zhuravlev <i.a.zhuravlev@cbtnet.ru>
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To: Harald Schmalzbauer <h.schmalzbauer@omnilan.de>
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Cc: freebsd-questions@freebsd.org
Subject: Re: MTU, fragmentation and Jumbo Frames question
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On 09.02.2010 20:12, Harald Schmalzbauer wrote:
> Hello all,
>
> I have 3 machines connected to an JumboFrame enabled switch.
> One FreeBSD 8-stable and two windows machines.
> I can send echo requests with payload of 8972 between the windows
> machines, but I don't get an answer from the FreeBSD machine. At the
> edge of 8130 bytes, the FreeBSD machine eats the packets without any
> error notification. A payload <= 8130 bytes works!
> All MTUs are set to 9000, interfaces are all intel em.
> Like mentioned, the ping between the two windows machines work like
> expected, beyond 8972 bytes payload the OS is fragmenting (resp. tells
> me that DF bit was set but fragmentation was needed)
> FreeBSD seems to never fragment packets, since I don't get an answer if
> I define payload greater than MTU. But this should work, shouldn't it
> (`ping -s 10000 host`)
>
> Does anybody have any explanation why pings are working up to 8130 bytes
> payload and are silently droped beyond that even my MTU ist set to 9000
> (and route get confirms the MTU 9000)?

kern/143285
but "ifconfig em0 -rxcsum" is enough for me.