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

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Date:	Fri, 25 Jul 2014 16:59:51 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	Zoltan Kiss <zoltan.kiss@...rix.com>,
	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 4:31 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> 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 layer drops it because the route is no longer valid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/
>

Besides that the cached dst by that socket should be obsolete as well,
since the old routing entry might not be valid any more. I mention this
because routing cache was removed between 2.6.32 and 3.10.
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