Today, 3,000 websites have made themselves reachable over IPv6 in order to participate in World IPv6 Launch. (Some have enabled IPv6 prior to today.) The 3,000 includes the top four in the Alexa Web ranking: Google, Facebook, YouTube, and Yahoo. Other notable converters include Bing, AOL, Netflix, Comcast, AT&T, Microsoft, NASA, Sprint, the US Geological Survey, Sony Japan, and Porsche.

Last year, many websites also enabled IPv6, but turned the new version of the Internet Protocol off again after 24 hours. After that test flight, the Internet Society and other organizers now deem IPv6 permanently ready for prime time: "the future is forever."

Additionally, a number of Internet Service Providers, such as Comcast and Time Warner Cable, have started enabling IPv6 for their consumers. But unlike publishing an IPv6 address for a website in the Domain Name System, giving broadband customers IPv6 access isn't accomplished with one flick of a switch. This is an ongoing effort. Last but not least, three makers of home routers (Cisco/Linksys, D-Link, and ZyXEL) now have models with IPv6 enabled out of the box available, in order to hook up to the IPv6-ready service of the aforementioned ISPs.

The existing Internet Protocol (IPv4) has 32-bit addresses, allowing for 3.7 billion usable addresses. That sounds like a lot, but it really isn't. For instance, the North American Number Plan allows for 6.4 billion phone numbers for just North America. And your iPod touch and desktop computer don't need a phone number, but they do need an IP address (it is possible to share). IP addresses are similar to phone numbers in that they're given out in large blocks, so unused numbers in Montana can't easily be used in New York. In practice, it's impossible to put every last address into use.

"It is very difficult to predict when IPv4 will run out in the North America," Curran told Ars. "We believe it could occur as early as the middle of 2013."

IPv6 fixes this problem by making the addresses 128 bits long. And just one extra bit means double the addresses. So 96 extra bits really fixes the problem. This is a good thing: the Asia-Pacific region ran out of IPv4 addresses a year ago and in Europe there's only 18 million left under the current rules (with between half a million and one million being used up every week). Daniel Karrenberg, chief scientist at the RIPE NCC, which distributes IP addresses in Europe, the Middle East, and the former Soviet Union, predicts that IP addresses will run out in the region around the end of September. North America has a bit more time. "It is very difficult to predict when IPv4 will run out in the North America, as it is based on requests from ISPs for additional space," John Curran, president and CEO of ARIN told Ars (ARIN is the RIPE NCC's counterpart in North America). "At this time we believe it could occur as early as the middle of 2013."

It's no secret that until now, IPv6 adoption has been lackluster to say the least. But today's effort is a big step forward: Alain Fiocco calculates on the Cisco Blog that no less than 27.2 percent of all US-based pageviews can now in principle happen over IPv6. The IPv6 statistics at the Amsterdam Internet Exchange—where many global, regional, and local ISPs exchange traffic—point in the same direction. Until now, IPv6 traffic would peak at around 2 gigabits per second, but today, most of the day saw 3Gbps worth of IPv6 traffic: 0.4 percent of the total AMS-IX traffic.

Of course, 3,000 participants out of millions of websites isn't much. Low, single-digit percentages of IPv6-enabled consumers at maybe two handfuls of ISPs in the US still leaves a lot of work to do until the entire Internet is IPv6-capable and IPv4 can be decommissioned. However, Leslie Daigle, chief Internet technology officer at the Internet Society, expects more organizations to jump on the IPv6 bandwagon in the wake of World IPv6 Launch. "One of the purposes of an activity like this is to give folks a date to shoot for," Daigle told Ars. "While thousands of websites, network operators, and home router vendors are participating in World IPv6 Launch today, we have heard, informally, that some organizations have stepped up their rollout plans and will be deploying IPv6 soon, even if they didn't make today's event. IPv6 is the new normal—we fully expect that IPv6 deployment will continue and simply become part of the normal course of how individuals and organization use the Internet."

In the meantime, current IPv4 networks continue to work as before. Organizations that don't have an immediate need for more IP addresses will be able to continue operating their networks based on IPv4. But ISPs need a continuous flow of fresh IP addresses to hand out to new customers. Ones with high growth have an especially tough decision to make once they run out of IPv4 addresses and new ones are no longer available from ARIN, the RIPE NCC, or APNIC in Asia and the Pacific.

Because 72.8 percent of the pageviews don't support IPv6 yet, giving new customers just IPv6 is not an option at this time. Address trading is a possibility, but certainly not a long-term one. Probably the most attractive option for ISPs that find themselves without enough IPv4 address space is to have multiple customers share a single IPv4 address through Network Address Translation (NAT). ISP-operated NATs are often called Carrier Grade NATs (CGNs).

NAT is already widely used in homes and enterprise networks to share one or a few "real" IPv4 addresses between several or even quite a lot of IP-capable devices. A side-effect of NAT is that incoming connections are no longer possible, but in consumer and enterprise settings, there are workarounds for that. This allows peer-to-peer applications such as VoIP, video conferencing, and the likes of BitTorrent to continue to work. However, if NAT is applied in the ISP network, it's likely that these applications, and possibly others, will no longer work well if at all. When this happens, these applications could move to IPv6 in order to keep working.

At that point, having IPv6 will be an advantage for those of us who want to run peer-to-peer applications or host services at home. For the ISPs, the advantage of offering IPv6 to their customers is that IPv6 traffic bypasses the CGNs, so fewer of those expensive boxes are necessary. Although today's effort doesn't have many immediate advantages, having a good amount of content available over IPv6 will start saving ISPs money within one or two years.

For website operators, the advantages of supporting IPv6 are a little less clear-cut. But with no CGNs in the middle, serving content to users over IPv6 could end up being faster and more reliable. Blocking users and reporting abuse is also a lot easier because users can be identified by (the first part of) their IPv6 address, rather than hide in the midst of their fellow CGN users. If ISPs make a single CGN cover a large geographic area, a CGN could also effectively hide the geolocation of the users behind it. In that case, IPv6 could allow a website operator to determine a user's location more precisely and reliably, which can be useful for advertising purposes.

So today's event is important as a big step toward IPv6 as a repair mechanism to fix IPv4 problems looming on the horizon. It's a bit like an oil change—it doesn't make your car run better today, but it sure helps prevent it from running a lot worse in the future.

Related reading: "The future is forever: the state of IPv6 in the Apple world," by Iljitsch van Beijnum