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Date:      Thu, 10 Apr 2008 09:27:19 -0700
From:      "Jack Vogel" <jfvogel@gmail.com>
To:        "Vitezslav Novy" <vnovy@vnovy.net>
Cc:        freebsd-current@freebsd.org, Steven Hartland <killing@multiplay.co.uk>
Subject:   Re: IP bad-len 0 ( on em0 )
Message-ID:  <2a41acea0804100927p327d0777waaf5c6cea8afdbfe@mail.gmail.com>
In-Reply-To: <47FDB51A.1030606@vnovy.net>
References:  <200802042142.38606.qpadla@gmail.com> <200802070018.54429.qpadla@gmail.com> <006801c87f19$a14d8060$b6db87d4@multiplay.co.uk> <200804092043.24500.qpadla@gmail.com> <2a41acea0804091659l7ac2d9adqcbdd0caf900469b@mail.gmail.com> <47FDB51A.1030606@vnovy.net>

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On Wed, Apr 9, 2008 at 11:35 PM, Vitezslav Novy <vnovy@vnovy.net> wrote:
> Jack Vogel wrote:
>
> > On Wed, Apr 9, 2008 at 10:43 AM, Nikolay Pavlov <qpadla@gmail.com> wrote:
> >
> > > On Thursday 06 March 2008 01:35:43 Steven Hartland wrote:
> > >  > Did you ever get anywhere with this? Did Jack respond?
> > >
> > >  Nope. I've disabled tso.
> > >
> >
> >
> > I've looked into this a little, and then got interrupted with other
> issues. The
> > reason the thing is zero'ed is because the hardware is going to
> repacketize
> > this big wad that its been handled, it should be making new headers that
> > appear in the packets on the wire. So its not  yet clear to me what the
> > real brokenness is, you are actually SUPPOSED to zero that value and
> > csum according to documentation, but the rewritten headers should have
> > correct len's in them, so the question is why in some cases they do not.
> >
>
>  I think packets on wire have correct IP-len, but after sending packet to
> card, driver injects original long packet with zeroed IP-len to BPF.
>  So in tcpdump, we see packet with zero IP-len.
>
>
>  vita
>
>
>

ahhh, yes, that makes sense, hmmm, suggestions on what to do about it?

Jack



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