Date: Fri, 12 Jan 2007 14:49:22 -0800 From: Chuck Swiger <cswiger@mac.com> To: "Bruce M. Simpson" <bms@FreeBSD.org> Cc: freebsd-net <freebsd-net@freebsd.org>, Ricardo Nabinger Sanchez <rnsanchez@wait4.org>, hugme@hugme.org Subject: Re: Problem with port 0 Message-ID: <9A4F1DBC-B536-4845-811B-8546E4201D69@mac.com> In-Reply-To: <45A807F8.7080603@FreeBSD.org> References: <f9876c510701120903r65543ef4nafc7eeead2becb42@mail.gmail.com> <20070112163057.2a3ec8f0.rnsanchez@wait4.org> <45A807F8.7080603@FreeBSD.org>
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On Jan 12, 2007, at 2:13 PM, Bruce M. Simpson wrote: > Ricardo Nabinger Sanchez wrote: >> But port 0 has special meaning to the kernel (ie, "give me some >> random >> port"). Also, it is a reserved one. Please check IANA: >> >> http://www.iana.org/assignments/port-numbers >> >> I'm afraid you'll have to select another port number. >> > Nope. A source port of 0 is perfectly legal for UDP. There's nothing in RFC-768 which forbids one from using a source or destination port of 0, but it also is true that IANA reserves 0/tcp and 0/udp for exactly the reasons Ricardo mentioned. I know that at least some firewalls will explicitly drop traffic using port 0 because it is expected that a well-behaved network stack will reassign a random ephemeral port rather than sending traffic out to or from port 0...YMMV. -- -Chuck
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