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

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Date:	Sat, 15 Mar 2008 09:51:35 +0100
From:	Gabriel Barazer <gabriel@...va.fr>
To:	Willy Tarreau <w@....eu>
CC:	netdev@...r.kernel.org
Subject: Re: [2.6.24.3][net] bug: TCP 3rd handshake abnormal timeouts

[corrected the netdev mailing list address]

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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