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Update: These scripts are no longer maintained. They have been superceded by the OpenWrtScripts repo

TL;DR These scripts test your network for bufferbloat, and configure your CeroWrt router.

  1. Test your network for bufferbloat from any Linux or OSX computer with and Both scripts require the netperf benchmark program from

  2. Configure a CeroWrt Router to a repeatable state with,, and

About CeroWrt

The CeroWrt router firmware project has largely eliminated the problem of bufferbloat on Ethernet for home routers. This algorithm makes a huge difference for wireless, too, although there's still more work to be done.

Bufferbloat is undesired latency that happens when routers buffer too much data during periods of high traffic. The symptoms of bufferbloat makes "the Internet feel slow." The Smart Queue Management (SQM) techniques based on the fq_codel algorithm developed by the CeroWrt team are being widely adopted across the Internet to make everyone's network performance better.

We developed the scripts below (sometimes also called "Ceroscripts") to measure the improvements to latency in as we worked on CeroWrt. These scripts include:

  • Scripts that measure the performance of your router or offer load to the network for testing.

  • Script to configure the CeroWrt router consistently after flashing factory firmware.

  • Script to set up a IPv6 6-in-4 tunnel to

  • Script to collect troubleshooting information that helps us diagnose problems in the CeroWrt distribution.

These scripts are bundled into the final CeroWrt build as the 'cerowrtscripts' package, saved in the /usr/lib/CeroWrtScripts directory. To get the newest versions, you can use opkg update; opkg upgrade

If the scripts are not built into your version of CeroWrt, it is safe to put them in that CeroWrtScripts directory.

This script emulates a web-based speedtest, but does it one better. During the download and upload, the script simultaneously measures latency of pings to see whether the data transfers affect the responsiveness of your network.

Here's why that's important: If the data transfers increase the latency/lag significantly, then other network activity, such as voice or video chat, gaming, and general network activity will also work poorly. Gamers will see this as lagging out when someone else uses the network. Skype and FaceTime will see dropouts or freezes. Latency is bad, and good routers will control it.

The script measures latency during data transfers. It will run on any computer where you can install the netperf software. To invoke it:

sh [ -4 | -6 ] [ -H netperf-server ] [ -t duration ] [ -p host-to-ping ] [-n simultaneous-streams ]

Options, if present, are:

  • -H | --host: DNS or Address of a netperf server (default -
    Alternate servers are netperf-east (east coast US), netperf-west (California), and netperf-eu (Denmark)
  • -4 | -6: Enable ipv4 or ipv6 testing (default - ipv4)
  • -t | --time: Duration for how long each direction's test should run - (default - 60 seconds)
  • -p | --ping: Host to ping to measure latency (default -
  • -n | --number: Number of simultaneous sessions (default - 5 sessions)

The output shows separate (one-way) download and upload speed, along with a summary of latencies, including min, max, average, median, and 10th and 90th percentiles so you can get a sense of the distribution. The tool also displays the percent packet loss.

Example: The example below shows two measurements on a a 7mpbs/768kbps DSL circuit. On the left is a test run without SQM; on the right is a test using SQM.

  • Without SQM, upload latency gets huge (greater than 5 seconds), meaning that network performance would be terrible for everyone during that time. In this test, there doesn't seem to be much bloat in the download direction, although it happens in many other circumstances.

  • With SQM, transmit and receive rates remain comparable to the no-SQM case, while latency only goes up a little in either directions (less than 27 msec under load).

Test results:

Example with NO SQM - BAD                                     Example using SQM - GOOD 

root@cerowrt:/usr/lib/CeroWrtScripts# sh   root@cerowrt:/usr/lib/CeroWrtScripts# sh
[date/time] Testing against (ipv4)    [date/time] Testing against (ipv4)
   with 5 simultaneous sessions while pinging        with 5 simultaneous sessions while pinging
   (60 seconds in each direction)                                (60 seconds in each direction)

 Download:  6.84 Mbps                                         Download:  6.91 Mbps
  Latency: (in msec, 58 pings, 0.00% packet loss)              Latency: (in msec, 61 pings, 0.00% packet loss)
      Min: 37.982                                                  Min: 38.696
    10pct: 41.002                                                10pct: 42.565
   Median: 57.647                                               Median: 54.135
      Avg: 54.814                                                  Avg: 54.097
    90pct: 62.689                                                90pct: 62.777
      Max: 64.680                                                  Max: 65.401

   Upload:  0.74 Mbps                                           Upload:  0.76 Mbps
  Latency: (in msec, 61 pings, 14.08% packet loss)             Latency: (in msec, 53 pings, 0.00% packet loss)
      Min: 39.213                                                  Min: 38.241
    10pct: 1404.113                                              10pct: 41.106
   Median: 3392.531                                             Median: 46.484
      Avg: 3244.456                                                Avg: 47.209
    90pct: 4546.094                                              90pct: 52.409
      Max: 5055.858                                                Max: 58.272

This script runs several netperf commands simultaneously. This mimics the stress test of Flent (formerly known as netperf-wrapper) but without the nice GUI result.

When you start this script, it concurrently uploads and downloads several streams (files) to a server on the Internet. This places a heavy load on the bottleneck link of your network (probably your connection to the Internet), and lets you measure both the total bandwidth and the latency of the link during the transfers.

To invoke the script:

sh [ -4 | -6 ] [ -H netperf-server ] [ -t duration ] [ -p host-to-ping ] [-n simultaneous-streams ]

Options, if present, are:

  • -H | --host: DNS or Address of a netperf server (default -
    Alternate servers are netperf-east (east coast US), netperf-west (California), and netperf-eu (Denmark)
  • -4 | -6: Enable ipv4 or ipv6 testing (default - ipv4)
  • -t | --time: Duration for how long each direction's test should run - (default - 60 seconds)
  • -p | --ping: Host to ping to measure latency (default -
  • -n | --number: Number of simultaneous sessions (default - 4 sessions)

The output of the script looks like this:

root@cerowrt:/usr/lib/CeroWrtScripts# sh
[date/time] Testing (ipv4) with 4 streams down and up 
    while pinging Takes about 60 seconds.
Download:  5.29 Mbps
  Upload:  0.39 Mbps
 Latency: (in msec, 64 pings, 1.54% packet loss)
     Min: 37.493
   10pct: 41.625
  Median: 61.724
     Avg: 63.557
   90pct: 84.536
     Max: 118.194

Note: The download and upload speeds reported may be considerably lower than your line's rated speed. This is not a bug, nor is it a problem with your internet connection. That's because the acknowledge messages for one stream can consume a significant fraction (as much as 25%) of the link's capacity in the opposite direction.

This script continually invokes the netperfrunner script to provide a long-running heavy load. It runs forever - Ctl-C will interrupt it.

This script updates the factory settings of CeroWrt to a known-good configuration. If you frequently update your firmware, you can use this script to reconfigure the router to a consistent state. You should make a copy of this script, customize it to your needs, then use the "To run this script" procedure (below).

This script is designed to configure the settings after an initial "factory" firmware flash. There are sections below to configure many aspects of your router. All the sections are commented out. There are sections for:

  • Set up the ge00/WAN interface to connect to your provider
  • Update the software packages
  • Update the root password
  • Set the time zone
  • Enable SNMP for traffic monitoring and measurements
  • Enable NetFlow export for traffic analysis
  • Enable mDNS/ZeroConf on the ge00 (WAN) interface
  • Change default IP addresses and subnets for interfaces
  • Change default DNS names
  • Set the SQM (Smart Queue Management) parameters
  • Set the radio channels
  • Set wireless SSID names
  • Set the wireless security credentials

To run this script

Flash the router with factory firmware. Then ssh in and execute these statements. You should do this over a wired connection because some of these changes may reset the wireless network.

ssh root@
cd /tmp
cat > 
[paste in the contents of this file, then hit ^D]
Presto! (You should reboot the router when this completes.)

Note: If you use a secondary CeroWrt router, you can create another copy of this script, and use it to set different configuration parameters (perhaps different subnets, radio channels, SSIDs, enable mDNS, etc).

This script configures CeroWrt to create an IPv6 tunnel. It's an easy way to become familiar with IPv6 if your ISP doesn't offer native IPv6 capabilities. There are three steps:

  1. Go to the Hurricane Electric site to set up your free account. There are detailed instructions for setting up an account and an IPv6 tunnel at the CeroWrt IPv6 Tunnel page.

  2. Edit the script, using the parameters supplied by They're on the site's "Tunnel Details" page. Click on the "Example Configurations" tab and select "OpenWRT Backfire 10.03.1". Use the info to fill in the corresponding lines of the script.

  3. ssh into the CeroWrt router and execute this script with these steps.

     ssh root@
     cd /tmp
     cat > 
     [paste in the contents of this file, then hit ^D]
     [Restart your router. This seems to make a difference.]

Presto! Your tunnel is up! Your computer should get a global IPv6 address, and should be able to communicate directly with IPv6 devices on the Internet. To test it, try: ping6

This script collects a number of useful configuration settings and dynamic values for aid in diagnosing problems with CeroWrt. If you report a problem, it would be helpful to include the output of this script.

By default, it collects information about the first 2.4GHz radio/interface, and writes the collected data to /tmp/cerostats_output.txt


A set of scripts spawned by the CeroWrt project




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