[ILUG] throttle control

[Dermot Buckley]

>   Anyone know how to get "tc" to do something like;
>     Stop port 80 traffic using more than 70% of bandwidth
>

Never really understood tc properly, but something along the lines of the
following should serve the purpose.

Firstly, mark every packet that you want throttled (i.e. everything not from
the lan which came from port 80).  With ipchains this would go something
like

	mylan=192.168.1.0/24
	ipchains -A output -i eth0 -s ! $mylan 80 -d $mylan -m 1

where eth0 is your internal interface (you can only control the output of an
interface - so this is where you catch the web traffic)

Now, say that eth0 is a 100Mbit card, your internet connection is 128kbit
and you want to limit the marked traffic to 96kbit (75%).

	tc qdisc add dev eth0 root handle 10: cbq bandwidth 100Mbit avpkt 1000
	tc class add dev eth0 parent 10:0 classid 10:1 cbq bandwidth 100Mbit rate
128kbit \
		allot 1514 weight 13kbit prio 8 maxburst 20 avpkt 1000

Note the 'bounded' in the next line (traffic in this class cannot exceed
this rate)

	tc class add dev eth0 parent 10:1 classid 10:100 cbq bandwidth 100Mbit rate
96kbit \
		allot 1514 weight 10kbit prio 5 maxburst 20 avpkt 1000 bounded
	tc qdisc add dev eth0 parent 10:100 sfq quantum 1514b perturb 15

Now send all the marked packets through the queue

	tc filter add dev eth0 parent 10:0 protocol ip prio 25 handle 1 fw classid
10:100


I'm not 100% on what all the values do :), but this does work (we use
something similar to throttle downloads).

And when you change your mind and decide you need the extra bandwidth to
download debian 2.2r4 :)

	tc qdisc del dev eth0 root


Would be interested myself in hearing from anyone who knows a bit more about
this stuff,

Dermot.