Simulating a slow connection with tc

Question

I have a linux box (Centos 5.5) on which I want to limit the network traffic. I have an application that we distribute to clients and I want to test it on the minimum recommended bandwidth of 256Mbit/sec. So far the tc tutorials I have seen seem to allow you to limit bandwidth according to certain criteria, but I want to limit the bandwidth in all situations (to/from all IP address, no matter what the IP header looks like, etc).

One tutorial suggested I use:

tc filter add dev eth0 protocol ip parent 10: prio 2 flowid 10:2

but I get the following error:

Unknown filter "flowid", hence option 10:2 is unparsable

Any ideas on how to limit bandwidth coming into/out of eth0 in all circumstances?

Answer 1

If you want to apply limitation to all outbound traffic, you don't need filters at all. Just add your qdisc to the interface root handle like so:

tc qdisc add dev eth0 root handle 1: tbf rate 256mbit latency 1ms burst 1540

If you want to shape/police inbound traffic, it's a little more complicated. You'll need to use e.g. an IFB interface:

modprobe ifb
ip link set dev ifb0 up
tc qdisc add dev eth0 ingress
tc filter add dev eth0 parent ffff: protocol ip u32 match u32 0 0 action mirred egress redirect dev ifb0
#  ^- this is a dummy filter, match u32 0 0 matches all traffic
tc qdisc add dev ifb0 root handle 1: tbf rate 256mbit latency 1ms burst 1540

---

Here's a different approach, using two simple filters:

tc qdisc add dev eth0 ingress
tc filter add dev eth0 root         protocol ip u32 match u32 0 0 police rate 256mbit burst 10k drop flowid :1
tc filter add dev eth0 parent ffff: protocol ip u32 match u32 0 0 police rate 256mbit burst 10k drop flowid :1

Answer 2

This might be a bit out of your scope, but WAN-emu has been very good at emulating environments with strange requirements for throughput and latency[1]

[1]: http://speed.cis.nctu.edu.tw/wanemu/ WAN-emu

Answer 3

You have add 1 ruler like this tc qdisc add dev eth0 root handle 10: htb default 20

affter that like your

tc filter add dev eth0 protocol ip parent 10: prio 2 flowid 10:2