Date: Thu, 30 Jan 1997 10:11:41 -0700 (MST)
From: David Borman <dab@BSDI.COM>
Message-Id: <199701301711.KAA16320@forge.BSDI.COM>
To: end2end-interest@ISI.EDU
Subject: Re: Frequency of RST terminated connections

(I've stripped down the To:/Cc: lines to just end2end-interest,
it was getting a bit long...)

> >It would be nice if port numbers were assigned in the stack,
> >rather than at the application, but they aren't. And without
> 
> Aren't they? I thought most BSD-derived and BSD-inspired stacks (i.e.,
> just about all of them) will automatically assign a local port number
> for you.  Yeah, you can override it, but few if any applications do so
> on a connect() as there is little if any reason to do so.

Just a minor nit... connect() is used to specify the remote address
and port, bind() is used to specify the local address and/or port.
If you don't do a bind(), or do a bind() with a zero port number,
then the kernel does the selection of the local port number.
 
Of greater concern to me is how 4.3 BSD and later based systems
divide up the port space, as defined in <netinet/in.h>
	1-1023		Reserved for privileged processes
	1024-5000	Dynamically assigned local port numbers
	5001-65535	User servers, not necessarily privilaged.
Having only 3977 ports available for the kernel to do dynamic
port number assignment means it is using just over 6% of the
total port number space.  It also isn't what was intended.  When
Mike Karels recently noticed that the range was only up to 5000,
not 50000, he thought "When did that get broken?", and a check of
the SCCS file showed that it had been broken since it went in,
a couple of months prior to the release of 4.3 BSD.  (Prior to
4.3, ports 1024-65535 were available to the kernel for dynamic
assignment.)

In looking at the current Port number assignments
	ftp://ftp.isi.edu/in-notes/iana/assignments/port-numbers
it looks like the ranges should be:
	1-1023		Well Known Ports
	1024-49151	Registered Ports
	49152-65535	Dynamic and/or Private Ports
which reserves the top 1/4 of the port number space for dynamic
allocation, just a bit over 4 times the space currently used by
BSD based systems.  BSDI is in the final stages of getting
BSD/OS 3.0 ready for release, so we won't be making any changes
at this point in time, however I plan on changing the dynamic
port assignment code in the kernel to use 49152-65535 for 3.1.

Is anyone aware of any systems out there that might break if we
start regularly using local ports that have the high bit set?

		-David Borman, dab@bsdi.com