Editing Traffic shaping with tc

Sometimes it's necessary to limit traffic bandwidth from and to a [[VE]].
You can do it using ordinary <code>tc</code> tool.

== Packet routes ==
First of all, a few words about how packets travel from and to a [[VE]].
Suppose we have [[Hardware Node]] (HN) with a VE on it, and this VE talks
to some Remote Host (RH). HN has one "real" network interface <tt>eth0</tt> and, 
thanks to OpenVZ, there is also "virtual" network interface <tt>venet0</tt>.
Inside the VE we have interface <tt>venet0:0</tt>.

<pre>
    venet0:0               venet0    eth0
VE >------------->-------------> HN >--------->--------> RH

    venet0:0               venet0    eth0
VE <-------------<-------------< HN <---------<--------< RH
</pre>

== Limiting outgoing bandwidth ==
We can limit VE outgoing bandwidth by setting the <tt>tc</tt> filter on <tt>eth0</tt>.
<pre>
DEV=eth0
tc qdisc del dev $DEV root
tc qdisc add dev $DEV root handle 1: cbq avpkt 1000 bandwidth 100mbit
tc class add dev $DEV parent 1: classid 1:1 cbq rate 256kbit allot 1500 prio 5 bounded isolated
tc filter add dev $DEV parent 1: protocol ip prio 16 u32 match ip src X.X.X.X flowid 1:1
tc qdisc add dev $DEV parent 1:1 sfq perturb 10
</pre>
X.X.X.X is an IP address of VE.

== Limiting incoming bandwidth ==
This can be done by setting the <code>tc</code> filter on <code>venet0</code>:
<pre>
DEV=venet0
tc qdisc del dev $DEV root
tc qdisc add dev $DEV root handle 1: cbq avpkt 1000 bandwidth 100mbit
tc class add dev $DEV parent 1: classid 1:1 cbq rate 256kbit allot 1500 prio 5 bounded isolated
tc filter add dev $DEV parent 1: protocol ip prio 16 u32 match ip dst X.X.X.X flowid 1:1
tc qdisc add dev $DEV parent 1:1 sfq perturb 10
</pre>
Note that <code>X.X.X.X</code> is an IP address of VE.

== Limiting VE to HN talks ==
As you can see, two filters above don't limit [[VE]] to [[HN]] talks.
I mean a [[VE]] can emit as much traffic as it wishes. To make such a limitation from the [[HN]],
it is necessary to use <tt>tc</tt> police on <tt>venet0</tt>:
<pre>
DEV=venet0
tc filter add dev $DEV parent 1: protocol ip prio 20 u32 match u32 1 0x0000 police rate 2kbit buffer 10k drop flowid :1
</pre>

== Limiting packets per second rate from VE ==
To prevent dos atacks from the VE you can limit packets per second rate using iptables.
<pre>
DEV=eth0
iptables -I FORWARD 1 -o $DEV -s X.X.X.X -m limit --limit 200/sec -j ACCEPT
iptables -I FORWARD 2 -o $DEV -s X.X.X.X -j DROP
</pre>
Here <code>X.X.X.X</code> is an IP address of VE

== External links ==
* [http://lartc.org/howto/ Linux Advanced Routing & Traffic Control HOWTO]

[[Category: HOWTO]]
[[Category: Networking]]