[LARTC] __Very__ Low Bandwidth

[Matthew Pearson <matthew.pearson@infomatrix.com>]

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 
below that I didn't get any traffic through. I've had a look at this 
generally, but couldn't find an answer. It doesn't even seem like the 
first reply packet gets through. I have tried it with much bigger 
buffers, but this doesn't help.

I found that if I put a web proxy on the machine that is running this, 
then the minimum I can turn the bandwidth down to is 12kbit and below 
that the web browser doesn't get anything back.

Is this because the delay is so great that things are getting thrown 
away by the kernel? Could I munge the packets to turn up the TTL or 
something similar?

Many thanks for some excellent tools.

Matthew Pearson

#!/bin/bash

CLIENT1\x192.168.1.190/32
CLIENT2\x192.168.1.191/32
OPER­d;
DEV=eth0
RATE=3kbit
PEAKRATE=3kbit
BUFFER1\x10kb
BUFFER2\x10kb

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 
240kbit

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

tc filter $OPER dev $DEV protocol ip parent 1:0 u32 match ip dst 
$CLIENT1 flowid 1:2
tc filter $OPER dev $DEV protocol ip parent 1:0 u32 match ip dst 
$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 
$CLIENT1 police rate $RATE buffer $BUFFER1 drop flowid :1

tc filter $OPER dev $DEV parent ffff: protocol ip u32 match ip src 
$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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