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Date:      Tue, 28 Jul 2009 07:15:32 +0100
From:      Mark Sandford <j.m.sandford@hotmail.co.uk>
To:        <freebsd-ipfw@freebsd.org>
Subject:   RE: Using dummynet to restrict bandwidth with more than 2 active pipes / queues
Message-ID:  <COL110-W1117070BA101EAA0AD722492150@phx.gbl>
In-Reply-To: <COL110-W10D341161C0B631FE5239892140@phx.gbl>
References:  <COL110-W10D341161C0B631FE5239892140@phx.gbl>

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Sorry if anyone's wasted time looking at this.  The problem appears to be w=
ith the traffic generator.  Once we get above two generation processes we t=
hink that the data is being sent in bursts so although it appears to be rig=
ht 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@hotmail.co.uk
mob: 07990 565976

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






> From: j.m.sandford@hotmail.co.uk
> To: freebsd-ipfw@freebsd.org
> Date: Mon=2C 27 Jul 2009 14:08:22 +0100
> Subject: Using dummynet to restrict bandwidth with more than 2 active pip=
es / queues
>=20
>=20
> Hi all=2C
>=20
> =20
>=20
> I've been using dummynet for a while to perform degraded network testing =
which has been really useful.
>=20
> =20
>=20
> Recently=2C 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.
>=20
> =20
>=20
> We are having throughput issues when more than 2 pipes are being used
> simultaneously. These issues appear to be independent of the bandwidths
> specified.
>=20
> For example:
> We set two traffic generators transmitting at 30Mbps across two of the br=
idges (pipes)=2C sending 1000 byte UDP packets (1042 bytes on the wire) for=
 a 20 second period.
>=20
> 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.
>=20
> We the capture on the far end and can see that bandwidth has been restric=
ted to 20Mbps as specified.  All good!  :o)
>=20
> The problem comes when we add any extra flows.
>=20
> The above example is repeated but with two extra traffic generators trans=
mitting at just one packet per second each across a further two pipes.
>=20
> Again we can see from the counters that the packets all arrive at ipfw=2C=
 however we only get 10Mbps at the receiving end (and we get a number of pa=
cket_drops logged at dummynet).
>=20
> We feel we must have missed something obvious but after over a week of re=
ading / testing we're running out of ideas.
>=20
> Is anyone able / willing to help?
>=20
> ~~~~~~~~~~~~~~~~~~~~~~~~
> Mark Sandford
>=20
> email: j.m.sandford@hotmail.co.uk
> mob: 07990 565976
>=20
> ~~~~~~~~~~~~~~~~~~~~~~~~
>=20
>=20
>=20
>=20
>=20
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