"Now we've just got a handful of people doing IPv6, but I fully expect to see a significant increase in IPv6 traffic" on World IPv6 Day, Brzozowski said. "It'll be a significant increase, but the traffic numbers are still going to be pretty small. We're not going to reach anywhere near the level of traffic we get for IPv4."
Comcast and other carriers are migrating to IPv6 because the Internet is running out of addresses using IPv4. The free pool of unassigned IPv4 addresses expired in February, and in April the Asia Pacific region ran out of all but a few IPv4 addresses being held in reserve for startups. The American Registry for Internet Numbers (ARIN), which doles out IP addresses to network operators in North America, says it will deplete its supply of IPv4 addresses this fall.
IPv4 uses 32-bit addresses and can support 4.3 billion devices connected directly to the Internet, but IPv6 uses 128-bit addresses and can connect up a virtually unlimited number of devices: 2 to the 128th power. IPv6 offers the promise of faster, less-costly Internet services than the alternative, which is to extend the life of IPv4 using network address translation (NAT) devices.
One major stumbling block for IPv6 deployment is that it's not backward compatible with IPv4. That means carriers such as Comcast and website operators such as Google have to upgrade their network equipment and software to support IPv6 traffic.
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