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

[Oleg Bulyzhin]

On Wed, Mar 04, 2009 at 08:17:05PM +0100, Sebastian Mellmann wrote:
> 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.
> 
> 
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If you have 7.1R or 6.4R setting net.inet.ip.dummynet.io_fast=1 will probably
reduce latency.

-- 
Oleg.

================================================================
=== Oleg Bulyzhin -- OBUL-RIPN -- OBUL-RIPE -- oleg at rinet.ru ===
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