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Date: Mon, 10 Mar 2008 22:26:39 +0100
From: Vitezslav Novy <vnovy@vnovy.net>
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To: Steven Hartland <killing@multiplay.co.uk>
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Cc: freebsd-current@freebsd.org, jfvogel@gmail.com
Subject: Re: IP bad-len 0 ( on em0 )
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Steven Hartland wrote:
> Did you ever get anywhere with this? Did Jack respond?
> 
> ----- Original Message ----- From: "Nikolay Pavlov" <qpadla@gmail.com>
> 
> On Wednesday 06 February 2008 19:12:20 Vitezslav Novy wrote:
>> >> Do you have set TSO flag on interface?
>> >
>> > Good catch. The problem is gone with net.inet.tcp.tso set to 0.
>> > But TSO is enabled by default in 7.0. Could this be a em driver bug?
>>
>> I don't know. I only saw this when researched another TSO related
>> problem.
>>
>> vita
> 
> May be Jack could say something about this?
> 

It is TSO related problem of em driver.
Affects only cards with adapter->hw.mac.type < e1000_82575.
During transmit function em_tso_setup is called and this function sets 
packet ip_len field to zero. (also ip csum)

After successful transmit, packet is injected to BPF with zeroed ip_len 
  field.


vita