netdev - Re: TCP connection closed without FIN or RST

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Date:   Fri, 3 Nov 2017 09:39:51 -0400
From:   Vitaly Davidovich <vitalyd@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: TCP connection closed without FIN or RST

On Fri, Nov 3, 2017 at 9:02 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2017-11-03 at 06:00 -0700, Eric Dumazet wrote:
>> On Fri, 2017-11-03 at 08:41 -0400, Vitaly Davidovich wrote:
>> > Hi Eric,
>> >
>> > Ran a few more tests yesterday with packet captures, including a
>> > capture on the client.  It turns out that the client stops ack'ing
>> > entirely at some point in the conversation - the last advertised
>> > client window is not even close to zero (it's actually ~348K).  So
>> > there's complete radio silence from the client for some reason, even
>> > though it does send back ACKs early on in the conversation.  So yes,
>> > as far as the server is concerned, the client is completely gone and
>> > tcp_retries2 rightfully breaches eventually once the server retrans go
>> > unanswered long (and for sufficient times) enough.
>> >
>> > What's odd though is the packet capture on the client shows the server
>> > retrans packets arriving, so it's not like the segments don't reach
>> > the client.  I'll keep investigating, but if you (or anyone else
>> > reading this) knows of circumstances that might cause this, I'd
>> > appreciate any tips on where/what to look at.
>>
>>
>> Might be a middle box issue ?  Like a firewall connection tracking
>> having some kind of timeout if nothing is sent on one direction ?
>>
>> What output do you have from client side with :
>>
>> ss -temoi dst <server_ip>
>
> It also could be a wrapping issue on TCP timestamps.
>
> You could try disabling tcp timestamps, and restart the TCP flow.
>
> echo 0 >/proc/sys/net/ipv4/tcp_timestamps
Ok, I will try to do that.  Thanks for the tip.
>
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