From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: TCP connection closed without FIN or RST
Date: Fri, 03 Nov 2017 06:02:47 -0700
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To: Vitaly Davidovich <vitalyd@gmail.com>
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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