netdev - Re: Internet-Draft on Port Randomisation

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Date:	Mon, 08 Sep 2008 21:58:44 -0700
From:	Stephen Hemminger <stephen.hemminger@...tta.com>
To:	Eugene Teo <eugeneteo@...nel.sg>
CC:	netdev@...r.kernel.org, Eugene Teo <eteo@...hat.com>
Subject: Re: Internet-Draft on Port Randomisation

Eugene Teo wrote:
> Has anyone read this Internet-Draft?
> http://www.gont.com.ar/drafts/port-randomization/draft-ietf-tsvwg-port-randomization-02.txt
>
> In this memo, there are descriptions of four different ephemeral port
> randomisation algorithms (see page 17).
>
> Algo #1 and #2 are simple port randomisation algorithms. Algo #3 is
> what we have in Linux. The memo suggested algorithm #4, double-hash
> randomisation algorithm, which is an improvement to algo #3 (see page
> 15).
>
> Does anyone have any thought about the improved algorithm? Is this
> worth implementing, 
No the added lock overhead of a global next free port array is not worth 
it. Think of big web server under
DoS pressure. The existing port search can run in parallel, Algo #4 was 
suggested by people
who don't work on a real SMP OS.
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