Comcast this month initiated the first North American test of IPv6 -- the next-generation Internet protocol -- running natively in a DOCSIS environment, with a group of cable modem users in Colorado.
The development comes as the address blocks for IPv4 have almost all been assigned to the Internet's regional registries, meaning that at some point this year service providers likely will be forced to begin more widely using IPv6.
IPv4 provides 4.29 billion unique addresses, whereas IPv6 provides an astronomically large address space of 2 to the 128th power.
Comcast implemented a "dual stack" configuration, in which the cable modems are able to natively access both IPv4 and IPv6 content and services without any translation.
"This is a tremendous milestone for Comcast, cable operators, DOCSIS technology and the Internet community at large," John Brzozowski, Comcast distinguished engineer and chief architect for IPv6, wrote in a blog post Monday.
Other MSOs and network providers are also actively getting prepared for the next-generation protocol.
Time Warner Cable, for its part, plans to begin residential IPv6 trials this spring and expects to adopt a dual-stack approach. The MSO signed up its first commercial customer using native IPv6 over its fiber-access product last year.
"Time Warner Cable has long been preparing for the eventual end of IPv4 address availability," chief technology officer Mike LaJoie said in a statement.
In Comcast's IPv6 test, the first 25 users went live Jan. 11, 2011. Since then, the MSO has expanded the number of users in Colorado and will soon expand to other parts of the country, according to Brzozowski.
Comcast is using cable modem termination systems and cable modems from Arris, as well as home networking equipment from Apple. All the equipment is running commercially available software.
In the test, each user has been allocated an IPv6 block that provides about 18 quintillion unique IPv6 addresses, "as a first step as we evaluate what will be the optimal IP address allocation size for our customers," Brzozowski wrote.
Comcast is providing additional information on the IPv6 trial at www.comcast6.net.