OCEAN CITY old News Item - rc5 is suitable for testing

Summary: After a week of testing in the lab, we are delighted to report that the last major bugs (#216 and #195) appear to be stomped in Cerowrt 1.0. While our testing continues, we welcome other testers to download the firmware and give the router a try! Originally published on 17 Aug 2011.

About CeroWrt

CeroWrt is a project to resolve endemic problems in home networking today, and to push the state of the art of edge networks and routers forward. Projects include tighter integration with DNSSEC, wireless mesh networking (Wisp6), measurements of networking and censorship issues (BISMark), among others, notably reducing bufferbloat in both the wired and wireless components of the stack.

CeroWrt’s Goals

CeroWrt is a build of the OpenWrt routing platform intended for use by individuals, network engineers, researchers, teachers, and students interested in advancing the state of the art on the Internet, and in particular, those investigating the problems of latency under load, bufferbloat, wireless-n, and the inter-relationships between various TCP & QoS algorithms.

CeroWrt breaks with home router conventions in several ways. CeroWrt comes with a high performance integral web server with which you can establish local web services and provide web content and services 24x7.

First class name services become a necessity rather than a “nice to have” with IPv6 deployment. Manual configuration of name services with IPv4 and IPv6 literal addresses is no longer feasible by most people, if indeed it ever was. Toward the goal of “plug and play” home environment able to publish IPv6 addresses into the global Internet name space without manual configuration, CeroWrt includes the Bind name server. Security in the home environment is also a goal, ergo CeroWrt’s support for DNSSEC using ISC Bind in a chrooted jail.

A core goal for CeroWrt is to provide a well understood platform, where contributors can perform tests with confidence that their results can be duplicated by others.

CeroWrt is the base on which other specialised builds may be built in the future. The default build is too big (~9MB) to be compatible with more commonly available routers.

There are other features all intended to help make insight into networking problems easier. In particular, bufferbloat, wherever we could find it, has been reduced, but not yet eliminated entirely; that requires the research in AQM and buffer management for which CeroWrt is intended.

Interesting features of this release:

Ocean City Release includes:

  • Extensive debloating
  • ISC Bind 9 with DNSSEC, running in a chroot jail
  • Numerous debugging and diagnostic tools
  • ECN is enabled
  • Multiple TCP algorithms (Cubic, Bic, Westwood+, Vegas)
  • Multiple traffic shapers (now including DRR and SFB)
  • Simulations are possible of packet loss and delay by using NETEM
  • Native, 6to4, and 6in4 IPv6 support
  • Mesh routing
  • The polipo web proxy
  • Local lighttpd Web Server
  • Rsync
  • Bridging different radios and ethernet has become very problematic, particularly in the face of multicast traffic and radically different wireless bandwidth. CeroWrt routes rather than bridges.
  • Many additional packages are not installed by default, but are available in the CeroWrt package repository.

While we have tried very hard to produce a usable web interface for the normal use of CeroWrt as your primary Internet router (and do desire you use it as such and give us feedback!), some things, such as configuration of the web proxy, or alternate TCP algorithms can require non-GUI editing via SSH.

As this is a research and development platform, there will be no long term support for this release and future RCs will likely require a complete reflashing and reconfiguration of your router. We apologize for the inconvenience but the state of the art and the problems we are trying to solve are rapidly moving targets that we must track closely. We will feed back the results of this work into stable distributions.

The Beta 1 “Ocean City” release (RC5)

CeroWrt is also aimed at (currently) a single hardware platform for which fully open drivers are available: the Netgear WNDR3700v2, a current 802.11abgn router using the Atheros AR7161 rev 2 with gigabit Ethernet ports. CeroWrt runs on the WNDR3700v2 only as it requires more than 8Mbytes of flash. Note that there may still be WNDR3700v1’s in the retail channel. Information on distinguishing them can be found in the bufferbloat wiki at http://www.bufferbloat.net/projects/bismark/wiki/Wndr3700v2

The Ocean City release is based on Linux; the DNS server is ISC Bind 9.8.0-P4 running from xinetd and in a chroot jail. RC5 is based on OpenWrt head of development as of commit 65dea0f0b144abbeb445c9d24a605aba506678a0, Thu Aug 11 13:52:40 2011 +0000.

Systematic testing of this software has just begun and the performance of the router is at this date unknown relative to other firmware.

Release candidate firmware can be downloaded from:


Installation directions can be found at:

Release notes are at:
http://www.bufferbloat.net/projects/cerowrt/wiki/OCEAN_CITY_RELEASE_NOTES IRC discussions on CeroWrt take place at irc.freenode.net: #bufferbloat
IRC discussions on OpenWrt in general take place on:irc.freenode.net: #openwrt

Mailing lists:

General discussion about CeroWrt takes place on the bloat-devel list found at:

General bufferbloat discussions can be found at:

Thanks for giving CeroWrt a try!

The network you save may be your own.

To edit this page, submit a pull request to the Github repository.
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Bufferbloat Related Projects

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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".