We have now started our pilot market deployment of IPv6, which is the first of several phases for our IPv6 deployment. This first phase will support certain types of directly connected CPE, where a computer is connected directly to a cable modem. This will depend upon the cable modem (a subset of DOCSIS 3.0 cable modems, which will expand over time) and will also depend upon the operating system (only Windows 7, Windows Vista, Mac OS X 10.7 / Lion), which must support stateful DHCPv6.
While this may seem like a small step, our approach, which is an incremental one, starts our deployment now and progressively widens it over time. This helps us to ensure the transition is orderly and stable, and that IPv6 performs as expected. Later phases will support home gateway devices (Apple, D-Link, Netgear, etc.) as well as our commercial fiber-based customers. Further, subsequent phases in 2011 and 2012 will support home gateway devices with variable length IPv6 prefixes.
For directly connected CPE, we will allocate an individual IPv6 address (/128), since we know that only a single device is connecting, with no additional need to subnet. When we begin our support for home gateway devices late this year, we initially plan to use a default IPv6 prefix allocation that is a /64 in length, providing over 18 quintillion IPv6 addresses. We have chosen this initial approach as it allows us to launch earlier than we otherwise could and most home routers today only support the use of a single /64 IPv6 prefix.
As we evolve our deployment for nationwide rollout in 2012, we plan to update our IPv6 allocations to provide shorter prefixes based on the type of service, devices in use by our subscribers, and the prefix size their device requests. We believe that offering a range of shorter prefix lengths (more IPv6 address space) is important to our customers, as this can enable multiple networks. We are highly committed to supporting such critical IPv6 functionality in the future, as support for variable prefix lengths improves.We plan to continue to assess address allocation policies as we deploy, particularly given how new IPv6 is from an operational standpoint globally.
The cable devices that will initially support IPv6 are listed at http://mydeviceinfo.comcast.net and are shown with a checkmark in the IPv6 column (click the top of the column to sort by that variable). This list will expand in the coming weeks and months as we complete testing of other devices.
It is also important to note that we are deploying native dual stack, which means a customer gets both IPv6 and IPv4 addresses. That means we are not using tunneling technology or large scale Network Address Translation (NAT). Using a tunnel introduces additional overhead compared to not using one (native IPv6), as your traffic must traverse a relaybefore going to the destination and back. And NAT technologies rely on two layers of NAT, one in your home (in a home gateway device), and one within a the service provider's network that usually shares a single IPv4 address across possibly hundreds of customers or more. Using NAT presents many challenges compared to not using NAT, as your traffic must traverse a NAT device before going to the destination and back. In addition, we believe those two layers of NAT will break a number of applications that are important to our customers.
In contrast to tunneling and large scale NAT, native dual stack avoids breaking or slowing applications and maintains a better and faster broadband Internet experience.
For a strategic view of this announcement, check out this complementary blog post today from Jason Livingood.