linux-kernel - Re: [2.6.24.3][net] bug: TCP 3rd handshake abnormal timeouts

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Message-ID: <47DB8D1C.7020006@oxeva.fr>
Date:	Sat, 15 Mar 2008 09:47:24 +0100
From:	Gabriel Barazer <gabriel@...va.fr>
To:	Willy Tarreau <w@....eu>
CC:	linux-kernel@...r.kernel.org, netdev@...nel.org
Subject: Re: [2.6.24.3][net] bug: TCP 3rd handshake abnormal timeouts

Hi

Thanks for the netdev Cc, I didn't know where to write to the "network 
guys".

By the way thanks for replying. It's hard to explain and describe a 
problem when you know people will ask you hundreds of questions related 
to application-level problems, or not reply because web/mysql problems 
are so common and generally not related to any kernel issue.

On 03/15/2008 7:58:49 AM +0100, Willy Tarreau <w@....eu> wrote:
> 
> You should carefully check the the SYN-ACK received by the client has a
> correct checksum ("cksum OK" in tcpdump output). It would be possible
> that for some reason, something on the network randomly corrupts it.

I used to use TCP offloading one time, and by the way never had a 
problem with it. Besides just to be sure, I have been able to reproduce 
the problem without any offload engine enabled (= not compiled into the 
kernel, mainly because it seems to hang the kernel at boot in 2.6.24.3). 
So I assume that is not the problem

I use wireshark to analyse my pcap files and it says the checksum is 
correct on all packets.

> Also, you say you have netfilter with conntrack. Is this on the client ?
> If so, you should try disabling it to rule out any possible bug in the
> connection tracking.

I have the conntrack  on both the client and server, and unfortunately 
can't disable it now on the client (I use it only for the REDIRECT 
target on a precise destination address and port, not MySQL related), 
however I will test today and disable it on the server, after I get some 
sleep (although I think the issue is on the client).

Gabriel
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