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Date: Wed, 2 Jun 2004 11:10:57 -0400
From: Barney Wolff <barney@databus.com>
To: Andre Oppermann <andre@freebsd.org>
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References: <20040602093940.N99493@atlantis.atlantis.dp.ua>
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cc: Dmitry Pryanishnikov <dmitry@atlantis.dp.ua>
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Subject: Re: net.inet.ip.portrange.randomized=1 hurts
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On Wed, Jun 02, 2004 at 12:41:51PM +0200, Andre Oppermann wrote:
> > have 16383 non-repeated port numbers before the first repeat).
> 
> The random generator indeed works badly.  If it was truely random it
> should generate a collision only every (1/range) on average.  Maybe
> the arc4random function reuses the same or small number of initial vectors
> all over again leading to the same small set of 'randomized' ports.

I believe you're seeing the birthday paradox at work, and the expected
number before collision is sqrt(N), not N.

Is the problem that the two systems have different ideas of MSL?

-- 
Barney Wolff         http://www.databus.com/bwresume.pdf
I'm available by contract or FT, in the NYC metro area or via the 'Net.