"My hope is that nothing happens on World IPv6 Day," Durand says. "The goal is to make sure that nothing happens and to build confidence that it is OK to deploy IPv6 and that IPv6 is not going to break the IPv4 Internet. We have been putting in place mechanisms to minimize the potential damage. This is the real learning from World IPv6 Day."
Most sites plan to turn off their IPv6 services when World IPv6 Day ends.
"It's a one-day experiment because we need to see how pervasive the problems are," Liu says. "If it turns out that the magnitude of the problem is bigger than ... we anticipated, then there is going to be some concerted effort to stamp out that behavior."
If World IPv6 Day goes as planned, participants predict that some websites will turn IPv6 on in production mode in the coming months.
"To see the momentum continue, we need to see more consumer electronic deploying IPv6, more content and more service providers adding subscribers," says John Brzozowski, distinguished engineer and chief architect for IPv6 at Comcast, which has an ongoing IPv6 trial. "I think we could see these announcements within weeks of the [World IPv6 Day] event ... depending on what we learn about IPv6 brokenness. If it wasn't really that broken after all, content providers may be more open to the idea of turning IPv6 on and leaving it on."
ISPs and content providers 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.