How is CeroWrt different from OpenWrt

Our goal is to build a test tool for the internet edge rather than a home router. Although CeroWrt can be used as such, it is not our primary goal. We encourage you to install the software on a spare router before committing to using it day to day - and compare it against your existing router, first. In the extensive testing, CeroWrt has been extremely reliable, faster than stock router firmware, and provides a good proof-of-concept that Bufferbloat can be conquered by simple, but powerful algorithms.

CeroWrt has incorporated the latest Linux 3.10 kernel modifications which have many defenses against bufferbloat. Other major differences between OpenWrt and CeroWrt:

  • all interfaces are routed, not bridged,
  • there is a full blown dnssec enabled server, with mDNS/Bonjour enabled for ease of device/service discovery,
  • the default naming scheme and default numbering scheme differ significantly from what you may be used to.

The Onboard documentation has far more detail as to what’s in the software.

Core things you should know

Default Password

The router has a default, rather than empty, password.

login: root
password: Beatthebloat

Do change it on installation, and even better, put your ssh key on it and disable password access entirely.

IP addresses & DNS

CeroWrt is a test platform, and as such we wanted it to co-exist within existing networks as best as possible, without conflicting with an existing network, and to not require NAT in order to function inside that network. NAT skews some test results horribly.

Since there is no public IP address space left, 10 networks are being increasingly used as backbone networks, and 192.168.X is most likely a number you are already using on your existing network, we chose the range to play in. The default address for the router is Each of the interfaces has a /27 subnet from this range by default - this allows 30 addresses per interface, a sensible limit for home/edge routers.

It is ironic that this is the last piece of ‘free’ IP address space left. See also BANA.

If you find this IP hard to remember or type, dns is enabled by default for a virtual subdomain of ‘home.lan. You should be able to get to it via gw.home.lan if you get dhcp from the router. Changing the default ip address ranges is difficult to do via the web interface and we suggest you stick with it for a while until you understand the reasoning, firewall, routing, and naming rules. (See DNS note below).

If you are running this inside your network, and not as your default gw, configure your default gw to statically assign an ip address, and route your subnet to the CeroWrt router, and turn off NAT.

See also the default naming scheme and default numbering scheme pages for more information.

Device/Interface Naming

We use an unusual device naming scheme to manage multiple kinds of wireless devices. Instead of using eth0, eth1, wlan0, etc. the interfaces have names that more accurately reflect their actual use. Prefixes use Wireless vs. Ethernet and Secure, Guest/Gateway, or DMZ. As noted above, each of these interfaces has a /27 subnet assigned. Thus:

  • ge00 is the Gateway Ethernet;
  • se00 is the first Secure Ethernet (LAN) interface;
  • sw00 is the first Secure Wireless interface at 2.4GHz;
  • gw10 is a Guest Wireless interface at 5.x GHz;
  • etc.

See also the default naming scheme and default numbering scheme pages for more information.

QoS - You NEED to set it

OpenWrt needs to set QoS for best performance. The defaults of CeroWrt work pretty well. Use the Setting Up SQM for CeroWrt 3.10 procedure for better results.

IPv6 is enabled BY DEFAULT

When connected to a real IPv6 address on a gateway, if CeroWrt doesn’t ‘just work’, we want to know about it.

To edit this page, submit a pull request to the Github repository.
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What Can I Do About Bufferbloat?
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Find us elsewhere

Bufferbloat Mailing Lists
#bufferbloat on Twitter
Google+ group
Archived Bufferbloat pages from the Wayback Machine


Comcast Research Innovation Fund
Nlnet Foundation
Shuttleworth Foundation

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".