Comcast Rolls Out Open Source Tech for IPv6

What will it take to get Americans to use IPv6 ?

For one thing, it will require broadband providers like Comcast (NASDAQ:CMCSA) to help users be fully enabled on IPv6 while still being able to access IPv4 content. That’s where the new open source Address Family Transition Router (AFTR) software comes into play.

AFTR is an open source effort led by Comcast and the Internet Systems Consortium (ISC), the developer of the BIND DNS server. The project aims to provide IPv6 users with continued access to IPv4 networks, helping to smooth the transition.

The IPv4 address space in North America is nearing exhaustion, which is why it’s becoming increasingly important for networks to move to IPv6, which provides more address space.

AFTR is part of a larger technology platform known as Dual-Stack Lite, which could prove to be the solution that helps users and carriers migrate to IPv6.

“The Dual-Stack Lite technology is made of two components — AFTR on the service provider side, and the B4 software interface on the home router side,” Rich Woundy, senior vice president of Software and Applications for Comcast, told “The expectation is that the Dual-Stack Lite B4 interface will become part of the standard package found on any home gateway in the future, both for those we will specify and those that our customers buy off the shelves.”

Woundy added that Dual-Stack Lite is not yet a production service offered by Comcast, but it is part of its IPv6 trial plans. Comcast began trial deployments of IPv6 for wholesale customers in 2009.

IPv6 addressing gets a kick-start for Comcast users

IPv6 addressing is different than IPv4 and as such, without some kind of additional technology, IPv4 addresses and content wouldn’t be fully accessible by IPv6 users.

That’s where a Dual-Stack Lite environment comes into play, hooking a residential broadband customer’s home gateway up with IPv6. However, doing so requires some work on Comcast’s end.

“When the customer sends IPv4 traffic, it is shipped through the B4 software interface on the home gateway inside of an IPv4-over-IPv6 tunnel to the AFTR box,” Woundy said. “That box will remove the IPv6 header and perform a traditional IPv4 NAT . The NAT pool of IPv4 addresses will be shared by a large number of customers.”

Still, Woundy noted that using AFTR and Dual-Stack Lite does not add significant additional performance overhead to a router.

“In Dual-Stack Lite, packets are transported as regular IPv6 packets on the native IPv6 access network,” Woundy said. “Only the home gateway and the AFTR box have to do a minimum amount of extra work to encapsulate/decapsulate the packets.”

Additionally, it doesn’t mean that the benefits of AFTR can’t make their way to other ISPs beyond Comcast, since the technology is open source.

“The AFTR code can work stand alone, but as with any technology, it needs to be tailored to the operator’s specific needs, for example to adapt to specific port usage reservation or port logging requirements,” Woundy said.

Sean Michael Kerner is a senior editor at, the news service of, the network for technology professionals.

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