netdev - Re: any way to let host act as TCP server OR client on same IP/port?

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Message-ID: <1310579520.2509.17.camel@edumazet-laptop>
Date:	Wed, 13 Jul 2011 19:52:00 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	netdev@...r.kernel.org
Subject: Re: any way to let host act as TCP server OR client on same
 IP/port?

Le mercredi 13 juillet 2011 à 10:30 -0600, Chris Friesen a écrit :
> I've been asked an interesting question about TCP.  We have some people 
> that want to set up a TCP socket that can listen for connections on a 
> given IP/port, but also initiate connections from that same IP/port. 
> (Only one at a time, of course.)
> 
> The TCP state machine seems to allow this (moving from LISTEN to 
> SYN_SENT) but it's not a normal transition.
> 
> Is there any way to do this using the socket API?
> 
> I thought up a hack whereby we could use NFQUEUE to detect an incoming 
> SYN and delay it while we call listen() on the socket.  Is there any 
> better way to do this?

Could you try SO_REUSEADDR, on both listener and connect attempt ?



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