Comcast 6RD Configuration Instructions for IPv6

6RD Configuration Instructions

IMPORTANT NOTE: On June 30, 2010, we activated 6RD border relays in our network as part of our testing of “Phase 1” of the expected transition to IPv6. On the one year anniversary of this activation, June 30, 2011, these 6RD border relays will be turned off, as they are no longer needed given the advanced state of our IPv6 testing and our Native Dual Stack strategy. Trial users testing 6RD can find directions on what to do next on our trial web forum. This date will of course enable our 6RD trial users to participate in World IPv6 Day on June 8, 2011.

As part of Comcast's IPv6 trials, we tested 6RD. On October 1, 2010, we announced the release of open source software for home gateway devices which supports 6RD, available here on SourceForge. This software is an extension of OpenWrt. While we have only tested it using the Linksys 160NL device, theoretically any device which is OpenWrt-capable, and with sufficient memory, should be able to run this software if you follow the configuration instructions below (until June 30, 2011). In addition, if your home gateway device already have 6RD support, you should also be able to follow these instructions and be able to use 6RD (until June 30, 2011).

General 6RD Configuration Settings

6RD Linksys 160NL Installation and Configuration
Additional FAQs:
General 6RD Configuration Settings
If you are using your own device or software to configure 6RD (other than our OpenWrt-based software), you can use this configuration:
  1. 6rd Prefix = 2001:55c
  2. 6rd prefix length = 32
  3. 6rd BR FQDN =
  4. IPv4 mask length = 0
6RD Linksys 160NL Installation and Configuration
The binary image for the 6RD client was developed on the OpenWRT 10.3 (Backfire) stream. Download it now here. This image includes the LuCI package, so you can use the web interface to setup all the necessary configuration parameters listed below. Note: We also provide the prebuilt binary for those who don’t want to compile the source tree. The binary is available here.

  1. You need a Cisco Linksys 160NL router (HW Version 1.0) running the original Cisco software image.
  2. You must have a public IPv4 address.
Flashing the Firmware
To start, connect to the device's website at Once there, go to the administration screen, and then firmware upgrade. Here you will upload the ".bin" file that you have compiled or downloaded (see this note).
NOTE: The factory 160NL username is typically blank (i.e. no username), and the factory password is typically "admin".
Once the upgrade is completed, reboot the device, then follow the directions below.

Configuring the 6RD Tunnel
  1. Login using the administrative GUI ( is the default address) and verify the version number at top right of the web page. It should show OpenWRT Backfire 10.03.
  2. On the login screen, type the username/password for the router and click the LOGIN button. The factory 160NL username is typically blank (i.e. no username), and the factory password is typically "admin".
  3. Click on Administrator tab in the right-hand corner. A 6RD tab will be displayed on the menu.
  4. Click on the 6RD tab.
  5. In Tunnel Type menu, select 6RD.
  6. You can choose between DHCP and Static options to set the 6RD parameters. We recommend you select Static.
  7. If you choose DHCP, you must configure your DHCP server to pass down the 6RD Option. Since IANA has yet allocated the DCHP option number for 6RD, we use 150, which will work fine until the reserved option number has been assigned by IANA.
  8. If you choose Static, you must enter the following parameters: IPv4 Mask Length (set to: 0), 6RD BR (set to:, 6RD Prefix (set to: 2001:55c) and 6RD Prefix Length (set to: 32).
  9. After parameters are filled, click Save & Apply. You may lose connectivity for few seconds as the router resets itself.
  10. The device will then automatically check the 6RD BR's health by pinging it. The tunnel will be setup only if the 6RD BR is reachable.
  11. If you want to know the 6RD Delegate Prefix, you can click on 6RDPrefixCalc. For this image, it doesn't support Prefix Delegation and so will always advertise a /64 to LAN.
  12. If you experience any IPv6 connectivity issues, please check the Tunnel Status section of the 6RD page to see if it is working. If you want to re-establish the tunnel, you can click the Reconnect button. This will tear down and re-create the 6RD tunnel.
Additional Configuration Notes
  • You should secure the device by setting a password. Click on System ---> Admin Password to set the password.
  • This image includes the wireless module and supports both 802.11g and 802.11n. This image also supports WPA/WPA2 encryption. You need to turn on wireless because it is off by default. You can configure wireless by clicking Administration to get to the Network menu. In Network, click the WiFi submenu and select RADIO0.
  • If you want to use a different DNS server from those learned from DHCP, you can goto Network ---> Interfaces ---> WAN menu. On the WAN page, goto Additional Field and choose DNS-Server. Hit Add button and a new field will be created. Enter the DNS server in the field and click Save & Apply.
  • This image supports UPnP and we have tested it successfully on many applications. You can enable UPnP by clicking Administration to access the Services menu. Under Services, there is UPNP submenu.
  • We tested this software with Xbox 360 Live (we're gamers). It worked when UPnP was enabled. You must also disable enable secure mode to get UPnP working for Xbox 360 Live. However, we couldn't connect to the PS3 Network. This seems to be a common issue for the OpenWRT base image.
Notes Concerning MTU Size
  1. Since 6RD is an encapsulation technology, it reduces the effective MTU size by the size of the encapsulated IPv4 header. We implemented the MSS option manipulation to increase the success rate for TCP connections. You can disable it by de-selecting MSS Option Rewrite
  2. Sometimes you may experience IPv6 connectivity issues even after enabling MSS Option Write. This can sometimes occur if the remote TCP server did not acknowledge the MSS Option. In this case, you may want to reduce the MTU size in your host to a lower value, which may mitigate the problem.
  3. We only recommend that advanced users configure the 6RD MTU size.
Is this built on OpenWrt?
This is built on OpenWrt "Backfire" code stream. It was fully integrated in the OpenWrt standard built process.

What does this software do?
This is an extension of OpenWrt, and it offers two different types of tunneling support. The first is where the user only has an IPv4 address and tunnels IPv6, using 6RD. The second is where the user only has an IPv6 address and tunnels IPv4, using Dual-Stack Lite.

What hardware was this tested on? Will it run on other hardware?
We have only tested this on the Linksys 160NL. However, the software should theoretically work on any device which is OpenWrt-capable, and with sufficient memory.

Where can I download the software?
You can download it here from SourceForge

What open source license did you use?

Why was this developed?
IPv6 transition technologies like 6RD are new, so when we started our IPv6 trials there was no commercially available home gateway available in retail with 6RD support. As a result, this software was developed for use in our IPv6 trials. The software is actively being used by customers in our network today, and is one of two different 6RD devices we are testing. The other device in our trial uses software developed by Cisco (which is not yet commercially released or supported).

Will Comcast continue to update this software?
In the near-term, yes. We may have one or two minor updates to resolve any bugs we uncover in our IPv6 trials. In the long-term we hope that others in the open source community will use and maintain the code, or that at least it will serve to assist other developers.

Do you offer technical support for 6RD?
No we do not. 6RD is part of our IPv6 trials. On or before the conclusion of these trials we will decide whether or not we will continue to maintain 6RD Border Relays, and if we do so, whether and what type of technical support may be offered.

When will the 6RD trial end?
The trial will conclude on June 30, 2011, exactly one year after it started.

Why is the 6RD trial ending?
Comcast's primary IPv6 strategy is Native Dual Stack and this is where we have chosen to focus our efforts moving forward after June 30, 2011. With this approach, native IPv6 addressing is available and there is no need to use 6RD.