CeroWrt 3.7 Release Notes

This release is obsolete. Please See the CeroWrt 310 Release Notes for the current release.

CeroWrt is a routing OS built on the OpenWrt firmware . It is a research project intended to resolve the bufferbloat epidemic in home networking today, and to push forward the state of the art of edge networks and routers. Subprojects include proper IPv6 support, tighter integration with DNSSEC, and most importantly, reducing bufferbloat in both the wired and wireless components of the stack.

The current CeroWrt release is code-named “Modena”, version 3.7.5-2 , built on 3 February 2013
Download the latest build from from http://snapon.lab.bufferbloat.net/~cero2/cerowrt/wndr/3.7.5-2/

CeroWrt Modena has proven to be highly stable, both from an ordinary operational standpoint as well as being able to survive heavy load testing. A number of people are using it as their primary router.


The CeroWrt 3.7 series of builds include the following features and capabilities:

  • Linux 3.7.5 kernel. Many of the fixes for bufferbloat are being implemented in this 3.7 kernel, so we are tracking these developments carefully. http://kernel.org
  • The CoDel algorithm from Kathie Nichols and Van Jacobson along with Eric Dumazet’s adaptation of Fair Queueing (fq_codel) on top. These in turn rely on the Byte Queue Limits that were implemented in the Linux 3.3 kernel. These techniques replace earlier Active Queue Management fixes for bufferbloat including: Stochastic Fair Queueing-Random Early Drop (SFQRED), but for comparison previous technologies such as SFQ and RED continue to be included.
  • Test releases of ns2_codel and nfq_codel - built on top of the current ns2 models of the code and not yet in mainline linux.
  • IPv6 support. Another major goal of CeroWrt is to make IPv6 networking in the home as simple as IPv4.
  • Babel mesh routing protocol (Quagga-babeld). Other protocols such as ra, ospf, and bgp are also available.
  • DNSSEC and DNSSEC proxying - Secure extensions to the DNS system. Proxying is currently in testing.
  • OpenWrt features. Because we track the OpenWrt code base carefully, we incorporate most of the capabilities of that distribution. We actively push our changes/enhancements back toward the OpenWrt trunk. http://openwrt.org
  • An attractive web GUI for configuration - LuCI
  • CeroWrt has the following packages either built-in and enabled, or optionally loaded:

IPv6 packages:
- radvd has been obsoleted as the new features in dnsmasq replace it
- dhcpv6-pd support
- dhcpv6 server support
- 6to4 version 9-1 - IPv6 tunnel through IPv4 (not turned on by default)
- 6in4 version 11-1 - IPv6 tunneling (not turned on by default)
- 6rd
- wide-dhcpv6-client replaced with the new features in dnsmasq

Other modules:
- strongswan4 4.5.3-2 - IPsec VPN http://www.strongswan.org/ - avahi-daemon 0.6.30-4 - reflector for zeroconf/mDNS-SD/Bonjour names http://avahi.org/ - samba36-server 3.6.5-2 - file and printer service http://www.samba.org - ntp 4.2.7p256-1 - network time client http://www.ntp.org/ - enhancements to the LuCI web GUI
- iptables - framework for packet filtering and network address/port translation
http://www.netfilter.org/ - iproute2 - utilities for controlling TCP/IP traffic in a Linux kernel http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2 - dnsmasq 2.66-13beta - DNS forwarder and DHCP server designed for home routers and NAT http://www.thekelleys.org.uk/dnsmasq/doc.html

Other measurement tools are available for installation:
- snmpd - for monitoring network traffic
- fprobe 1.1-1 for monitoring NetFlow traffic
- iperf 2.0.5-1
- scamper


3.7.5-2 “Modena”

Bind9 is obsoleted
Openvpn will be available in a later release

Experimental stuff

  • ns2_codel, nfq_codel, efq_codel available optionally
  • wifi queuing boosted from very low values to a compromise that preserves more bandwidth
  • debloat change to lower target to 5ms, quantums to 1000


  • bind removed
  • 6to4 fixes for interface assignment
  • 6to4 route propagation workaround (#406)
  • AQM gui module removed (too confusing, wasn’t working stuff)

Experimental Stuff

  • wifi queuing kept at low values
  • debloat change to lower target to 5ms, quantums to 256 (from mtu)
To edit this page, submit a pull request to the Github repository.
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Dec 3, 2022 Wiki page
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More about Bufferbloat
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What Can I Do About Bufferbloat?
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Bufferbloat Related Projects

OpenWrt Project
Congestion Control Blog
Flent Network Test Suite
The Cake shaper
CeroWrt (where it all started)

Network Performance Related Resources

Jim Gettys' Blog - The chairman of the Fjord
Toke's Blog - Karlstad University's work on bloat
Voip Users Conference - Weekly Videoconference mostly about voip
Candelatech - A wifi testing company that "gets it".