netdev - Re: "Listenless" TCP over NAT?

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Message-ID: <20080905121504.GJ7908@solarflare.com>
Date:	Fri, 5 Sep 2008 13:15:06 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	xerces8 <xerces8@...n.net>
Cc:	Linux Netdev <netdev@...r.kernel.org>,
	Linux Networking <linux-net@...r.kernel.org>
Subject: Re: "Listenless" TCP over NAT?

xerces8 wrote:
> Hi!
> 
> Recently someone mentioned on this (or maybe other...) list a seldom used
> technique of establishing a TCP connection without one host listening on a port,
> but but acting as "clients" and connecting to the peers port.
> 
> My question: Can this be used to establish a TCP connection between two hosts that
> are both behind a (P)NAT router ?
> 
> (the idea being: NAT router lets outgoing connections thru, and in this case both
> NAT router would  see an "outgoing" connection)
> 
> If yes, this would simplify the life of many users :-)

It's a bit more complicated than that.  See
<http://en.wikipedia.org/wiki/TCP_hole_punching>.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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