netdev - Re: TCP socket timeout after IP address is removed

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Date:	Fri, 25 Jul 2014 16:31:35 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Joby Poriyath <joby.poriyath@...rix.com>
Subject: Re: TCP socket timeout after IP address is removed

On Fri, Jul 25, 2014 at 1:04 PM, Zoltan Kiss <zoltan.kiss@...rix.com> wrote:
> Hi,
>
> We have a timout problem on TCP sockets, which probably has some trivial
> solution, but I couldn't figure it out after hours of staring at the code,
> so hopefully someone can shed some light on it here.
> The scenario is the following:
> - I start an ssh connection from host A to B, it works fine
> - netstat shows the socket is using local address K
> - then I remove local address K, and with DHCP I get a new one, L on a
> different interface (interfaces are always up during the whole time)
> - the socket is still alive, but my SSH connection doesn't transmit
> anything, obviously, as netstat says it is still using IP address K
> - ftrace showed me the data goes through the TCP layer and finally the IP
> layer drops it because the route is no longer valid
>
> On 3.10 kernel it times out after ~15 minutes or so, which isn't too good
> for me. On 2.6.32 it times out after a couple of minutes, and I would like
> to achieve the same, but I couldn't figure out how. Could anyone give me
> some guidance?

Depending on your scenario, you can either try tweaking the sysctl
net.ipv4.tcp_retries2 or use setsockopt TCP_USER_TIMEOUT

man tcp or see http://patchwork.ozlabs.org/patch/62889/


>
> Regards,
>
> Zoltan Kiss
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