Using dummynet to restrict bandwidth with more than 2 active pipes / queues

[Mark Sandford]

Sorry if anyone's wasted time looking at this.  The problem appears to be with the traffic generator.  Once we get above two generation processes we think that the data is being sent in bursts so although it appears to be right averaged over a second at a finer granularity the burstiness is meaning it's either exceeding the bandwidth or idle at each point.

~~~~~~~~~~~~~~~~~~~~~~~~
Mark Sandford

email: j.m.sandford at hotmail.co.uk
mob: 07990 565976

~~~~~~~~~~~~~~~~~~~~~~~~






> From: j.m.sandford at hotmail.co.uk
> To: freebsd-ipfw at freebsd.org
> Date: Mon, 27 Jul 2009 14:08:22 +0100
> Subject: Using dummynet to restrict bandwidth with more than 2 active pipes / queues
> 
> 
> Hi all,
> 
>  
> 
> I've been using dummynet for a while to perform degraded network testing which has been really useful.
> 
>  
> 
> Recently, we wanted to measure the performance limits of it on our
> hardware. To do this we setup a machine with 8 interfaces paired into 4
> ethernet bridges.
> 
>  
> 
> We are having throughput issues when more than 2 pipes are being used
> simultaneously. These issues appear to be independent of the bandwidths
> specified.
> 
> For example:
> We set two traffic generators transmitting at 30Mbps across two of the bridges (pipes), sending 1000 byte UDP packets (1042 bytes on the wire) for a 20 second period.
> 
> These are passed through dummynet pipes set up to restrict the bandwidth to 20Mbps at the bridge and we can see from the ipfw counters that all the packets hit the right rules and only the right rules.
> 
> We the capture on the far end and can see that bandwidth has been restricted to 20Mbps as specified.  All good!  :o)
> 
> The problem comes when we add any extra flows.
> 
> The above example is repeated but with two extra traffic generators transmitting at just one packet per second each across a further two pipes.
> 
> Again we can see from the counters that the packets all arrive at ipfw, however we only get 10Mbps at the receiving end (and we get a number of packet_drops logged at dummynet).
> 
> We feel we must have missed something obvious but after over a week of reading / testing we're running out of ideas.
> 
> Is anyone able / willing to help?
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~
> Mark Sandford
> 
> email: j.m.sandford at hotmail.co.uk
> mob: 07990 565976
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
> 
> 
> 
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