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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.

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7 Answers 7

33

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)

7
  • Yes, this is a very good module for these things, indeed. I can't believe noone answered this until now...
    – E Dominique
    Apr 28, 2009 at 9:37
  • I use this for testing servers locally (on localhost) as it's been standard on all distros for years. To add 20ms delay "tc qdisc add dev lo root handle 1:0 netem delay 20msec", and to remove it "tc qdisc del dev lo root"
    – pixelbeat
    Aug 30, 2009 at 23:16
  • 1
    Quick note: the kernel module is sch_netem. Generally there's no need to load it manually, it will be loaded automatically as needed.
    – sleske
    Dec 29, 2010 at 0:41
  • Here's working link linuxfoundation.org/collaborate/workgroups/networking/netem Apr 19, 2012 at 2:43
  • My version of netem (Ubuntu 13.10) also has the option to limit the bandwidth using the rate option: tc qdisc add dev lo root handle 1:0 netem delay 10ms rate 1mbit limit 1000. Note that for some devices such as lo (for accessing localhost), you need to set the queue length as well: ifconfig lo txqueuelen 1000. See serverfault.com/a/394949/76090
    – z0r
    Nov 20, 2013 at 2:58
28

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.

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  • Thanks for this tip. For some reason trickle wouldn't work for me with firefox but it worked fine with google-chrome. (Ubuntu 9.10 64bit)
    – Tom
    Feb 18, 2010 at 18:52
  • 7
    trickle works by intercepting calls to link in standard library functions for TCP transfers - if an app has these functions statically linked in at compile time then this can not work. Aug 9, 2010 at 13:34
17

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.

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  • 1
    This is not quite what the OP is looking for (it's about conserving bandwith, not about purposefully degrading the connection), but still good to know.
    – sleske
    Dec 20, 2010 at 9:41
  • 1
    BTW: It's package wondershaper in Debian.
    – sleske
    Dec 20, 2010 at 9:41
  • This rocked b/c we were having problems at the office with bandwidth saturation, there was a backing going that I couldn't interrupt, and I was able to fix this in two simple lines: # apt-get install wondershaper then # wondershaper eth0 9999999 500 thanks again!
    – orange80
    May 13, 2011 at 20:59
  • 4
    wondershaper appears to have some math problems though. To get a 1Mb/s up/down path, we ended up using 28096 instead of 1024. No idea as to why this happened though.
    – boatcoder
    May 14, 2012 at 20:19
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    To reset, use: sudo wondershaper clear eth0
    – Léo Lam
    Jan 18, 2015 at 18:33
8

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.

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  • NistNet is not updated in a long time, is it? IMO, the best way by far is the netem module, which already exists in all recent kernels.
    – E Dominique
    Apr 28, 2009 at 9:35
  • You may be able to simulate a machine with 2 NICs using a VM.
    – Scott
    Apr 28, 2009 at 14:50
  • link doesn't work
    – hasen
    Aug 30, 2009 at 20:18
  • Link works for me.
    – tripleee
    Oct 5, 2012 at 3:49
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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.

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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.

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3

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.

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  • 1
    This is exactly for what I am looking! Huge thanks. I'm glad I scrolled down and kept reading. Jul 15, 2016 at 13:57

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