From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andy Furniss <andy.furniss@dsl.pipex.com>
Date: Fri, 07 Apr 2006 21:46:19 +0000
Subject: Re: [LARTC] __Very__ Low Bandwidth
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References: <442D44FE.7070105@infomatrix.com>
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To: lartc@vger.kernel.org

Matthew Pearson wrote:
> I am using the script below to simulate a very low bandwidth connection. =

>  I found that I could turn the bandwidth knob down to about 4kbit, but=20
> below that I didn't get any traffic through. I've had a look at this=20
> generally, but couldn't find an answer. It doesn't even seem like the=20
> first reply packet gets through. I have tried it with much bigger=20
> buffers, but this doesn't help.
>=20
> I found that if I put a web proxy on the machine that is running this,=20
> then the minimum I can turn the bandwidth down to is 12kbit and below=20
> that the web browser doesn't get anything back.
>=20
> Is this because the delay is so great that things are getting thrown=20
> away by the kernel? Could I munge the packets to turn up the TTL or=20
> something similar?
>=20
> Many thanks for some excellent tools.
>=20
> Matthew Pearson
>=20
> #!/bin/bash
>=20
> CLIENT1=192.168.1.190/32
> CLIENT2=192.168.1.191/32
> OPER=ADd;
> DEV=3Deth0
> RATE=3D3kbit
> PEAKRATE=3D3kbit
> BUFFER1=10kb
> BUFFER2=10kb
>=20
> echo -e "Attach Egress policy..."
> tc qdisc $OPER dev $DEV root handle 1:0 htb default 15
> tc class $OPER dev $DEV parent 1:0 classid 1:1 htb rate 240kbit
>=20
> tc class $OPER dev $DEV parent 1:1 classid 1:2 htb rate 240kbit ceil=20
> 240kbit
> tc class $OPER dev $DEV parent 1:1 classid 1:3 htb rate 240kbit ceil=20
> 240kbit
> tc class $OPER dev $DEV parent 1:1 classid 1:15 htb rate 240kbit ceil=20
> 240kbit
>=20
> tc qdisc $OPER dev $DEV parent 1:2 handle 2:0 tbf rate $RATE burst $RATE =

> limit $BUFFER1 peakrate $PEAKRATE mtu 1600

I don't really get using tbf under htb - but it may be OK.

The reason it fails <12kbit is because you use it for burst - which is a=20
buffer length so <12kbit won't pass a 1500 byte packet.

Andy.
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