ipfw pipes: theoretical speed vs. reality

[Justin Bennett]

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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?

Thanks,

Justin
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