Brzozowski said Comcast has to give a /64 set of IPv6 addresses because that's the only size of IP address blocks that CPE supports today. He said Comcast will re-number its initial home gateway customers with shorter prefixes of IPv6 addresses once home gateway makers have compliant, interoperable products that support this feature.

"We have no intention of staying fixed on /64s," Brzozowski said. "Our goal is to get something out sooner rather than later, then we'll go back and incrementally introduce support for shorter prefixes. Maybe later this year we will be prepared to have Version 2 of our home networking service with shorter prefixes."

Until recently, home gateways have been a major stumbling block for ISPs like Comcast that are trying to deploy IPv6 because the devices lacked support for the new standard. Home gateways are mini-routers with firewall capabilities that consumers use to create networks in their homes, connecting PCs, tablets, TVs and gaming systems to the Internet.

"IPv6 home networking support is generally improving," Brzozowski says, pointing out that three months ago only one home gateway model sufficiently supported IPv6 and now there are six involved in Comcast's home networking service. "The upgrade of home networking equipment is still required. Some customers may require the purchase of new hardware or a software upgrade."

Added Lee Howard, director of network technology at Time Warner Cable: "Less than 1% of home gateways have IPv6. I can't rely on home gateways, instead I have to rely on the 15% of people that have no home gateway and plug directly into cable modems for my initial IPv6 deployment."