problem simulating a LFN

[Ian FREISLICH]

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

--
Ian Freislich