Subject: Re: TCP keepalives ignored by kernel when the contain timestamps

From: Charles Bearden <[email-masked]>
Date: Fri, 10 Jun 2011 11:39:33 -0500

On 06/10/2011 11:17 AM, Eric Dumazet wrote:
> Le vendredi 10 juin 2011 à 11:07 -0500, Charles Bearden a écrit :
>
>> You are correct: the checksums in the keepalives are broken, though they are
>> correct in the other segments from the Win2008 server. I have updated the pastes
>> linked to above with 'tcpdump -v' output. I apologize for missing that problem
>> the first time around.
>
> Hmm, maybe its OK : If checksums are offloaded to NIC, tcpdump 'lies'
> telling checksum is not OK, since tcpdump get a copy of the packet
> before being handled by the NIC.
>
> You should take a tcpdump on the receiving machine (the machine that
> apparently doesnt react to the keepalive probes)

I should have made this clear before: these dumps were captured on the machine 
that is ignoring the keepalives ("Ubuntu.host" in the dumps) from the other host 
("Win200[38].host" in the dumps). If I understand tcp checksum offloading 
correctly, it wouldn't play a role here.