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Date:      Mon, 18 Dec 2006 08:27:59 +0200
From:      Ian FREISLICH <>
To:        Looza <>
Subject:   Re: problem simulating a LFN 
Message-ID:  <>
In-Reply-To: Message from Looza <>  of "Sun, 17 Dec 2006 17:31:53 PST." <> 

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Looza wrote:
> Hi,
> I'm trying to simulate a LFN(Long Fat Network) to test various TCP versions.
> I am using iperf on the end PCs. I'm trying to use FreeBSD's ipfw to
> simulate a LFN.
> ex. throughput=1 Gbit/s and delay=100ms, trhoughput=100 Mbit/s and delay=1s
> This is how my hardware is connected.
> |Linux PC|--Gigabit--| FreeBSD box |--Gigabit--|Linux PC|
> With this configuration:
> >ipfw 500 add allow ip from any to any
> I get speeds of about 200 to 300 Mbit/s and the CPU usage goes up
> to 99%.  I've googled this problem and it seems that some good
> quality NIC do most of the processing so that the CPU doesn't have
> to. Unfortunately I have bad quality NICs so the CPU does all the
> processing, stoping the throughput at these speeds.

Try sysctl net.inet.ip.fastforwarding=1 .  With this set I can
formard and filter in excess of 500kpps using less than 5% CPU on
a Xeon.

I highly recomend the Intel 82546GB chip based adaptors (em driver).


Ian Freislich

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