Simulating a bad internet connection
I'm developing an embedded device which has access to the internet through LAN. I'm in the testing phase now, and I would like to test how the device performs when the connection to the internet is poor. Currently, the device is connected to a router through a hub, which I use to monitor the packets with Wireshark. What's the best way to throttle down the internet speed of the device to mimic a scenario that may happen?
Can I do it through a PC? Do I need access to the router? If so, is it possible to limit the speed of each IP in the router interface?
Actually, a friend suggested that I will purchase a usb2lan ethernet card, and to bridge the PC lan connection to the embedded device, and then using a software QoS limiter. do you think it will work ?
Answer
If you have a Mac handy, Macs have kernel facility called dummynet built in, which you control through ipfw. It allows you to simulate a slow connection, randomly drop packets with certain probabilities, and more.
The same facility exists in Linux and other OSes.
From the dummynet homepage:
As of Feb.2010 we have released the third major version of dummynet, which now runs on all main platforms: FreeBSD, Mac OS X as part of the native distributions, and you can find Linux, OpenWRT and Windows versions here.
It can do a lot for you:
limit the total incoming TCP traffic to 2Mbit/s, and UDP to 300Kbit/s
ipfw add pipe 2 in proto tcp
ipfw add pipe 3 in proto udp
ipfw pipe 2 config bw 2Mbit/s
ipfw pipe 3 config bw 300Kbit/s
limit incoming traffic to 300Kbit/s for each host on network 10.1.2.0/24.
ipfw add pipe 4 src-ip 10.1.2.0/24 in
ipfw pipe 4 config bw 300Kbit/s queue 20 mask dst-ip 0x000000ff
simulate an ADSL link to the moon:
ipfw add pipe 3 out
ipfw add pipe 4 in
ipfw pipe 3 config bw 128Kbit/s queue 10 delay 1000ms
ipfw pipe 4 config bw 640Kbit/s queue 30 delay 1000ms