netdev - tcp: how to prevent connection abort due to failed keepalive?

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Message-ID: <20140430142214.GB5108@eerihug-hybrid.rnd.ki.sw.ericsson.se>
Date:	Wed, 30 Apr 2014 16:22:15 +0200
From:	Erik Hugne <erik.hugne@...csson.com>
To:	<netdev@...r.kernel.org>
CC:	Anders Franzen <anders.franzen@...csson.com>
Subject: tcp: how to prevent connection abort due to failed keepalive?

Is there a way to disable connection termination due to failed TCP keepalives?
I was hoping that it would be possible to use TCP_KEEPCNT == 0 for this purpose,
but this gave back an -EINVAL.

There's nothing in the RFC that claims that closing the connection if the peer
fails to respond to _all_ probes, just that:

(RFC1122 section 4.2.3.6)
	It is extremely important to remember that ACK segments that
	contain no data are not reliably transmitted by TCP.
	Consequently, if a keep-alive mechanism is implemented it
	MUST NOT interpret failure to respond to any specific probe
	as a dead connection.

So, if we have a connection with TCP_KEEPCNT set to 1, and the peer fails to
respond to this "specific probe". I think the RFC is pretty clear that the
connection shall not be considered dead. In this case, Linux send a TCP RST
and aborts the connection.

//E
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