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>