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Date:      Wed, 05 Nov 2003 14:35:14 -0800
From:      Michael Nadler <>
Subject:   Re: maximum pipes in dummynet?
Message-ID:  <>
In-Reply-To: <>
References:  <>

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   The basic problem you are having is with ipfw, not merely dummynet.
   ipfw uses a linked list to hold the rules.  Every packet must be
   matched against these rules using a linear search.  And this search
   happens in the interrupt thread.  Packets that match none of the rules
   end up having the worst latency.  There is an inverse relationship
   between the number of packets and the number of rules.
   In my experience, 4000 ipfw rules is quite a lot.  We had to implement
   a custom modification to ipfw, creating a special class of static
   rules that were handled similar to the dynamic rules.  This mod
   permitted more than 100,000 rules with litte performance degredation.
   The ipfw pipe rule, just like a regular rule, can match multiple
   ports.  See ipfw(8).

Date: Wed, 5 Nov 2003 10:59:50 -0800
From: Yuchung Chen
Subject: maximum pipes in dummynet?
To: [1]
Cc: [2]
Message-ID: [3]<>
Content-Type: text/plain; charset=us-ascii

Hi all,

I am using dummynet to simulate many different links. After dummynet seems
to slow down after more than 4000 (static) pipes. That is, the link delay
is more than the specified delay.  My config file looks like

ipfw add 1 pipe     7 tcp from 10003 to out
ipfw pipe     7 config bw 730KByte/s queue 40 delay 4ms plr 0.01
ipfw add 1 pipe     8 tcp from to 10003 in
ipfw pipe     8 config bw 730KByte/s queue 40 delay 4ms plr 0.01
ipfw add 1 pipe     9 tcp from 10004 to out
ipfw pipe     9 config bw 1400KByte/s queue 40 delay 28ms plr 0.00
ipfw add 1 pipe    10 tcp from to 10004 in
ipfw pipe    10 config bw 1503KByte/s queue 40 delay 28ms plr 0.00

My machine is 2.66 P4 w/ 1G mem. Does anybody know how to make dummynet
support more pipes?

Also is it possible to specify one pipe for more than one port? i.e.,
ipfw add 1 pipe 10 tcp from to 10004,10537,3045 in





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