netdev - Re: TCP connection closed without FIN or RST

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Date:   Fri, 03 Nov 2017 06:00:10 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vitaly Davidovich <vitalyd@...il.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: TCP connection closed without FIN or RST

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>