Unfortunately, neither IPv4 or IPv6 are incompatible, which means that any IPv4 device will have to be assigned an IPv6 number. IPv4 to IPv6 connections will either have to be translated or tunneled, like a VPN connection, via a router.
And that means that the IPv4-to-IPv6 transition will likely be anything but simple. "The response that the global Internet industry will undertake an overnight transition to use IPv6 is perhaps at one somewhat improbable end of a rather broad spectrum of possibilities here, if only from the consideration of the implausibility of such timing in a network of tis [sic] size," Huston wrote.
However, the transition will likely be easier for some countries than others. According to OECD data collected in March, Germany, Japan, France, and Australia lead in terms of the number of IPv6 domains actually deployed; the United States is thirteenth, with 0.62 percent of the overall domains. Japan already has several IPv6 networks already deployed. About half of the top-level domains are IPv6 enabled.
Several solutions have been suggested to increase the pool of IPv4 addresses, ranging from market-based allocation, which could increase the cost of registering a new domain and benefit enterprises at the expense of users; seeking out "expired" blocks of IP addresses registered by defunct companies; or "seizing" blocks that are held but not used.
The bad news is that one of the easiest ways to forestall the exhaustion of these IP addresses is already in wide use: network address translation. The premise of the IP protocol, and especially IPv6, was to give each device on the network its own IP address. A PC connected to a NAT router receives its own sub-address, forcing the router to manage the packets flowing in and out of it, and assigning each to the proper PC. But since the router is an intermediary that requires some intelligence, router makers have added firewalls to sniff the packets further, and try and prevent hackers from penetrating the home network.
To date, virtually no home router supports IPv6; typing in "IPv6" on Netgear's Web page, for example, returns no results. But replacing the manufacturer firmware with a third-party application like Tomato does allow a determined user to add IPv6 support, although in that case the router becomes a bridge.
However, both Windows Vista and Windows Server 2003 both support IPv6 to some extent. By using Internet Connection Sharing, a Vista PC can act as a "6to4" router, using the IPv4-based Internet as a whole as just a cloud to tunnel an IPv6 connection through, encapsulating the traffic with an IPv4 header. A complementary technology called "Teredo," part of Windows Vista, was designed as a last resort for IPv6 connectivity, allowing a PC behind a NAT to tunnel to another NAT-protected device across the Internet. "As more IPv4 NATs are upgraded to support 6to4 and IPv6 connectivity become ubiquitous, Teredo will be used less and less, until eventually it is not used at all," according to Microsoft.
That makes measurement of IPv6 traffic extremely difficult. According to the Amsterdam Internet eXchange, the amount of IPv6 traffic is just 0.1 percent of the total. But IPv6 traffic tunneled using IPv4 protocols could mean that much more is being used, just beneath the surface.
Some companies have already bit the bullet. Comcast, for example, has already rolled out IPv6 from its core backbone out to its cable modem termination systems in 2007. However, the project required four years, and is still ongoing. "The primary lesson from Comcast's transition to IPv6 is the importance of planning ahead," the OECD concluded.
