[LARTC] __Very__ Low Bandwidth

[Matthew Pearson]

Thank you Andy. I'll have another look at it and change the values to 
get it to do what I need. Again, thank you.

Matthew Pearson

Andy Furniss wrote:
> 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 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=192.168.1.190/32
>> CLIENT2=192.168.1.191/32
>> OPER=add;
>> DEV=eth0
>> RATE=3kbit
>> PEAKRATE=3kbit
>> 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 
>> 240kbit
>>
>> 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 
> buffer length so <12kbit won't pass a 1500 byte packet.
> 
> Andy.