Google buys a lot of "dark fiber" (unused fiber-optic capacity) and many people take guesses at their reasons. Alex Lightman, CEO of IP telephony vendor Innofone.com, thinks that Google prepares for IPv6 era. IPv6 will replace IPv4 internet protocol as it will support much more internet addresses. As the number of devices connected to internet grows exponentially, IPv4 + NAT routers will not be enough.
"You know who else has a big pot of slash 20? Google," Lightman said. "Yahoo does too. It's not that service providers aren't doing it — it's the savvy service providers, with the high multiples and visionary management, that are getting ready to go into it. This is why Google bought mobile dark fiber. It's to go out and go: 'All these bozos in America aren't rolling out IPv6, so we'll do it if they aren't going to'."
Another reasons for buying dark fiber might be: Google Video's infrastructure, Google Wi-Fi and Google's data centers.