66

Is there a way to constrain the bandwidth on a NIC in linux? I'd like to be able to simulate an arbitrarily slow connection.

Tamara Wijsman
  • 57,881
Mark Borgerding
  • 968

7 Answers7

35

The netem kernel module, controlled by iproute.

You need to compile Netem with the kernel:

Networking -->
   Networking Options -->
     QoS and/or fair queuing -->
        Network emulator

Once the netem module loaded, iproute's tc allows you things like:

tc qdisc add dev  tap0 root netem delay 50ms loss 50%

(50 % packet loss, extra delay of 50 ms)

bortzmeyer
  • 1,191
32

Client side, right?

trickle should do what you want. If you're running Ubuntu (or Debian, I think), you can install it with sudo apt-get install trickle, and then run it. trickle -s -d 10 -u 10 firefox (or so, I haven't used it in a while) would run firefox, limiting its download and upload speed to 10 kilobytes a second.

Bernard
  • 716
18

I found a way to avoid my box from eating all the bandwidth available on network using a tool called 'wondershaper' in ubuntu. I hope it exist in other linux destros too. I can limit the bandwidth what my linux home pc can consume using following command. 

sudo wondershaper eth0 1000 200

This limits the download limit to 1000 kilobits and uplaod to 200 kilobits. Refer to the man pages of wondershaper for more information/options.

harry
  • 631
9

NIST make a network simulator called NistNet.

http://snad.ncsl.nist.gov/nistnet/ (link seems dead)

http://cs.ecs.baylor.edu/~donahoo/tools/nistnet/

NistNet lets you make a router that emulates a comms link of your choosing.

For simplest operation you have it on a box with two NIC's between two networks.

For example, I had an application that had to work over a satellite link.

Data could go over the a 2Mbps link with BIG latency. Control had to go over a 128kbps link, with the same latency.

NistNet helped to get it all working on 128kbps.

Using NistNet I could simulate not only the bandwidth, but also the latency, and it will also drop packets for you, simulating a busy or unreliable link.

If you want to simulate an abitrary connection, don't just constrain the bandwidth, wind the latency up too.

Don't forget to fragment packets either. You can set nice small MTU's on the phony link.

IIRC adding packet jitter will let you find out if you can cope with out-of order packets.

Tim Williscroft
  • 705
5

I've personally used wondershaper in the past for this, though it was written for an opposite use case - making the most of your ADSL connection.

I'll have to try the others mentioned here though.

Thomas Vander Stichele
  • 210
  • 1
  • 4
4

You can use locally installed squid proxy to limit bandwidth for example to test a web page on slow link:

  1. Install squid proxy from your distribution — on my Fedora it was as easy as yum install squid.

  2. Add the following to /etc/squid/squid.conf:

    delay_pools 1
    delay_class 1 1
    delay_access 1 allow all
    delay_parameters 1 16000/16000

    This will limit bandwidth to about 128 kbps (16000 Bps).

  3. Start squid: /etc/init.d/squid start

  4. Configure your browser to use proxy server localhost port 3128.

Tometzky
  • 486
4

No one has yet mentioned ip_relay, named "iprelay" in the Debian repositories. It works as a TCP proxy, rather than intercepting calls the way trickle does, and will work with any application that can use a proxy (e.g. a web browser) or accept a user-defined destination port (telnet, ssh, ftp, curl, et cetera).

It's a little more difficult to set up, but often works in situations where trickle won't.

CodeGnome
  • 2,131