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Date: Tue, 4 Jan 2011 15:52:53 +0100
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: nangergong <nangergong@gmail.com>
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Cc: freebsd-ipfw@freebsd.org
Subject: Re: How to obtain fixed packet loss ?
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On Mon, Jan 03, 2011 at 06:22:54PM +0000, nangergong wrote:
> Hi, all:
> 
>   As far as I know, in dummynet, plr is prabability-based, namely, when a
> packet is processed, it will be discarded according to the probability. So,
> if I have 100 packets and the plr is 5%, eventually I may just discard 3
> packets or even 1 packets. So, the real packet loss is not consitent with
> the plr-set value. Is there any good method that can give me a consistent
> packet loss? Thank you!

you would need to modify the "prob" option in ipfw so that
e.g. you specify a bitmap indicating the pattern of packet pass/drop

(this was the way i originally implemented packet loss back in 1995!)

cheers
luigi

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