Sometimes it's necessary to limit traffic bandwidth from and to the VPS. You can do it using ordinary tc tool.
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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 eth0 and, thanks to OpenVZ, there is also "virtual" network interface venet0. Inside VPS we have interface venet0:0.
venet0:0 venet0 eth0
VE >------------->-------------> HN >--------->--------> RH
venet0:0 venet0 eth0
VE <-------------<-------------< HN <---------<--------< RH
Limiting outgoing bandwidth
We can limit VE outgoing bandwidth by setting the tc filter on eth0.
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
X.X.X.X is an IP address of VE.
Limiting incoming bandwidth
This can be done by setting the tc filter on venet0:
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
Note that X.X.X.X 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 tc police on venet0:
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
Limiting packages per second rate from VE
To prevent dos atacks from the VE you can limit packages per second rate using iptables.
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
X.X.X.X is an IP address of VE