From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Pearson <matthew.pearson@infomatrix.com>
Date: Fri, 31 Mar 2006 15:04:30 +0000
Subject: [LARTC] __Very__ Low Bandwidth
Message-Id: <442D44FE.7070105@infomatrix.com>
List-Id: <lartc.vger.kernel.org>
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To: lartc@vger.kernel.org

I am using the script below to simulate a very low bandwidth connection.=20
  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.

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.

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?

Many thanks for some excellent tools.

Matthew Pearson

#!/bin/bash

CLIENT1=192.168.1.190/32
CLIENT2=192.168.1.191/32
OPER=ADd;
DEV=3Deth0
RATE=3D3kbit
PEAKRATE=3D3kbit
BUFFER1=10kb
BUFFER2=10kb

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

tc class $OPER dev $DEV parent 1:1 classid 1:2 htb rate 240kbit ceil 240kbit
tc class $OPER dev $DEV parent 1:1 classid 1:3 htb rate 240kbit ceil 240kbit
tc class $OPER dev $DEV parent 1:1 classid 1:15 htb rate 240kbit ceil=20
240kbit

tc qdisc $OPER dev $DEV parent 1:2 handle 2:0 tbf rate $RATE burst $RATE=20
limit $BUFFER1 peakrate $PEAKRATE mtu 1600
tc qdisc $OPER dev $DEV parent 1:3 handle 3:0 tbf rate $RATE burst $RATE=20
limit $BUFFER2 peakrate $PEAKRATE mtu 1600

tc filter $OPER dev $DEV protocol ip parent 1:0 u32 match ip dst=20
$CLIENT1 flowid 1:2
tc filter $OPER dev $DEV protocol ip parent 1:0 u32 match ip dst=20
$CLIENT2 flowid 1:3

echo -e "Attach Ingress policy..."
tc qdisc $OPER dev $DEV handle ffff: ingress

tc filter $OPER dev $DEV parent ffff: protocol ip u32 match ip src=20
$CLIENT1 police rate $RATE buffer $BUFFER1 drop flowid :1

tc filter $OPER dev $DEV parent ffff: protocol ip u32 match ip src=20
$CLIENT2 police rate $RATE buffer $BUFFER2 drop flowid :2

echo -e "Status Information:\nShowing QDiscs...\n"
tc qdisc show

echo -e "Showing classes...\n"
tc class show dev $DEV
echo -e "Showing filters...\n"
tc filter show dev $DEV
echo -e "Finished.\n"
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