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Re: Purpose of Port 0.

2017-02-20 02:54:05
On 2/20/17 12:30 AM, Danny Niu wrote:
Hi, all.

Recently on the POSIX mailing list, there's a discussion on the
correct way to bind to (or listen on) an ephemeral port. While I
referenced the "UNIX Network Programming", we're not quite satisfied
because even though it's co-written by someone involved in IETF, it's
still JUST a textbook.

The canonical way to do this, according to some (from
stackoverflow.com, and other places), is to bind to port 0, which I
assume had been reserved for this purpose, but I haven't find
anything to back this up yet.

On the POSIX list, they suggested that IETF should, (or should have
already) state(d) that port 0 be reserved for binding to ephemeral
ports. So can we find any reference for this? Or should we draft an
RFC?

The original convention is from berkeley sockets api, so it's been that
way since 1983 or so. it would predate therefore ieee 1003 by some
years. I would. suspect that Postel et al were well aware that it was
employed by that convention when it was noted as reserved in rfc 1340/1700.

Thanks.



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