ipfw (dummynet) adds delay, but not configured to do so

[Sebastian Mellmann]

Hi everyone!

I hope this is the right place to ask.

I've got a IPFW ruleset that looks like this:

cmd=ipfw
bottleneck_bandwidth=100Mbit/s
in_if="em0"

$cmd pipe 500 config bw $bottleneck_bandwidth
$cmd add pipe 500 all from any to any via $in_if

When I do a simple ping from one machine to another (actually the
FreeBSD machine is between those machines), I can see a delay of ~2ms.
Without any rules/pipes I've got under 1ms delay.

The question is:
Why do I have such a "high" delay though I didn't configure any "delay"
in my pipe?
Where does this additional millisecond come from (processing delay for
the packet in the pipe?)?
If I configure another rule (or like 10 more rules) that matches the
packet, I can see the delay increasing.
For example a delay of ~20ms, when I configure 10 pipes.
Am I doing something wrong?

Thanks in advance for any help and please tell me if you need additional
informations (e.g. kernel configuration).


Regards,
Sebastian M.