IPv4 uses 32-bit addresses and can support 4.3 billion devices connected directly to the Internet. Most IPv4 addresses have been handed out. The free pool of unassigned IPv4 addresses was depleted in February, and the that it has doled out all but its last 16.7 million IPv4 addresses which are being held in reserve for startup network operators.

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IPv6, on the other hand, uses 128-bit addresses and supports a virtually unlimited number of devices -- 2 to the 128th power. But despite its promise of an endless supply of address space, IPv6 represents only a tiny fraction -- less than 0.03% -- of Internet traffic.

Ulevitch said the new OpenDNS IPv6 service would allow Internet users to access IPv6-only websites, which he admits are a "very,very small'' portion of Internet resources.

OpenDNS says it has more than 20 million users globally, representing 1% of all Internet users. The company's free service is popular with U.S. public school systems, while its paid enterprise version has attracted corporations of all sizes.