ipfw pipes: theoretical speed vs. reality

[Julian Elischer]

Justin Bennett wrote:

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> All,
>
> I have recently been setting up pipes to shape bandwidth on our local 
> net.
>
> However, unless I am missing something, the TCP overhead seems quite 
> large.
>
> If I configure the following pipe:
>
> $IPFW pipe 1 config bw 64Kbit/s
> $IPFW add 31 pipe 1 ip from 192.168.0.1/24 to any
> $IPFW add 32 pipe 1 ip from any to 192.168.0.1/24
>
> The run traffic from my machine (192.168.0.2) through it, I get less
> than half the expected bandwidth (3.9KB/s). I tried another test with a
> 512Kbit/s pipe, and got around 30KB/s.
>
> I know on most ATM/FR lines, you can expect about 10% overhead, but 50%
> seems high.
>
> When I remove the pipe, my T1 comes back to life, and I can pull the
> same data at 160+KB/s.
>
> Am I missing something? 


yes you are queuing data in both directions on the same queue, thus 
serialising it..

use 2 seprarate pipes. one for each direction.


>
>
> Thanks,
>
> Justin
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