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"We could turn on IPv6 today and have users hit it, but we don't think it would be seamless," says Adam Bechtel, vice president of infrastructure at Yahoo.
Web sites such as Yahoo are upgrading their Web servers, load balancers and software to support IPv6 because the Internet is running out of address space using IPv4.
IPv4 uses 32-bit addresses and can support 4.3 billion devices connected directly to the Internet. IPv6, on the other hand, uses 128-bit addresses and supports a virtually unlimited number of devices - 2 to the 128th power.
Less than 5% of the world's IPv4 address space remains unallocated, and experts predict that the remaining IPv4 addresses will be assigned from the central pool to the regional registries in February. Regional registries, in turn, are expected to hand out the remaining blocks of IPv4 addresses to network operators by October.
Once IPv4 addresses are depleted, Web sites will need to either support IPv6 or use complex mechanisms such as carrier-grade network address translation (NAT) to communicate with IPv6-based users.
Yahoo has been working on IPv6 development since 2008, but in the last year it has become the company's second-largest IT infrastructure project. Only ongoing tech refresh efforts are costing Yahoo more engineering time and effort these days, executives say.
"In 2010, we rolled IPv6 into a corporate program called IP Survivability. We're taking a two-pronged approach. We need to stretch out our IPv4 usage longer, as well as get to the point where we can deploy IPv6. We probably have around 100 to 150 people involved," Fesler says.
Yahoo has IPv6-enabled routers deployed, supports IPv6 peering with other carriers, and has connected one of its data centers to the Internet via IPv6. In order to serve up IPv6 content, the company's engineers developed software for address translation, caching and proxying - dubbed the Yahoo Traffic Server - that it provided to the Apache Foundation last year as open source code.
"We have the Yahoo Traffic Server up and running, but we don't have it available to end users yet," Bechtel says. "We're still in the process of vetting it and getting our processes in line to make sure we get all the kinks worked out."
Bechtel describes IPv6 as presenting "an immense, immense set of challenges" for a Web site with as much traffic as Yahoo's.
"The network piece is pretty far along for most, but you've got all the operational pieces and the instrumentation," Bechtel says. "One out of every 2,000 users is going to have some level of brokenness. There are issues that carrier-grade NATs are going to introduce with the aggregation of IP addresses. The issue of geo-targeting is very significant, too... IPv6 is touching a lot of our people."
Yahoo is hoping that it can deploy IPv6 on its main Web site without having to rely on DNS whitelisting, a technique that Google has deployed to serve up IPv6 content only to users who are known to have end-to-end IPv6 connectivity and no IPv6 brokenness.