IP bad-len 0 ( on em0 )

[Vitezslav Novy]

Jack Vogel wrote:
> On Wed, Apr 9, 2008 at 10:43 AM, Nikolay Pavlov <qpadla at 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