Date: Mon, 01 Dec 2014 07:26:37 -0800 From: Yuri <yuri@rawbw.com> To: Daniel Corbe <corbe@corbe.net> Cc: freebsd-net@freebsd.org Subject: Re: Can multiple apps listen for TCP on the same port? Message-ID: <547C88AD.40407@rawbw.com> In-Reply-To: <20141201150225.GB64370@apollo.corbe.net> References: <547C5DD3.90604@rawbw.com> <20141201150225.GB64370@apollo.corbe.net>
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On 12/01/2014 07:02, Daniel Corbe wrote: > Generally the answer to your question is no. Two applications cannot > occupy the same port on the same protocol at the same time. > > To expand on this answer and to hopefully shed some light on why the > behavior you're observing with your application is absolutely correct; > the calling application (in this case, nc) has to explicitly call bind(2) > before it can begin accepting connections. If that port is already in > use then the call to bind(2) will fail. And in your case I suspect nc > is simply choosing to silently fail. Here the question is what does it mean "occupy the port"? The first instance isn't listening any more. The listening socket was closed. Why the presence of the socket that was accepted from (now closed) listening socket in the first instance is considered "occupying it"? Actually no system call in the second instance ever fails. Yuri
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