In hindsight, we reached peak IPv4 two years ago. The good news is that IPv6 is doing very well—but not nearly well enough. Is the IPv6 glass 1 percent full or 99 percent empty?

"Hi, I'd like to sign up for Internet service at my new apartment."

"That's great! We have the highest speeds at the best prices, you won't be disappointed. But unfortunately, last week Europe ran out of IPv4 addresses. We still have plenty of IPv6, though."

"IPv6? So I can use that to visit all my favorite websites, use IM and VoIP, download podcasts, and watch videos?"

"Well..."

Luckily, I escaped this conversation when recently signing up for an Internet connection. But if I move again next year or even the year after, I could end up with a faster Internet connection that is less functional, because it will no longer let me connect to every other Internet user. All because we ran out of numbers, which don't even cost anything. Sadly, not having them will cost us a lot of time, money, and effort as some cling to IPv4 and others adopt IPv6—by choice or otherwise—over the next few years.

Where we stand

First, let's look at IPv4. Five Regional Internet Registries (RIRs) give out IP addresses in different parts of the world. APNIC (Asia, the Pacific, and Australia) ran out in April of 2011, and this past September the RIPE NCC (Europe, the Middle East, and the former Soviet Union) did the same. As a result, the number of IPv4 addresses given out this year is about a third of what it was in 2010: only 80 million.

(The statistics are derived from files the five RIRs publish on their FTP sites every day. However, the ARIN numbers didn't look right, so I replaced them with those found here. This also changes the earlier reported totals for previous years.)

So ISPs and other users of IPv4 addresses in the RIPE and especially APNIC regions have to make do with whatever is left in their own pipelines—which typically hold six months' to two years' worth. There's a final block of 1024 addresses, or they have to do some trading.

ARIN (North America) has 45 million addresses left and gave out 24 million IPv4 addresses this year. So barring unforeseen events, ARIN will be in a situation similar to those of APNIC and the RIPE NCC in the first half of 2014. LACNIC (Latin America and the Caribbean) also has about a year and change until IPv4 addresses run out, while AFRINIC (Africa) has enough for several more years.

Back in 1994, Microsoft's Christian Huitema looked into networks running out of address space, coming up with an "HD ratio." This is the logarithm of the number of systems connected to the network divided by the logarithm of the number of possible addresses. Experience with several different networks showed that an HD ratio of up to 80 percent was reasonable, 85 percent painful, 86 percent extremely painful, and 87 percent the practical maximum.

According to the ISC Domain Survey, there were 909 million systems present in the Domain Name System (DNS) as of July 2012 (resulting in an HD ratio of 93 percent). Obviously, that is well beyond that practical maximum. In this sense, IPv4 is like a tube of toothpaste that's almost empty: every day, if you squeeze hard enough, a little more will come out. But at some point it's easier to just buy a new one.

Now, with IPv4 in decline, surely IPv6 must be ready to pick up the slack? Yes and no. Yes, IPv6 is doing incredibly well compared to even one or two years ago, but... it's not enough.

IPv6 refresher

IP addresses are 32 bits in size, which means there can be some four billion of them. In the early 1990s, the Internet Engineering Task Force (IETF) realized the Internet was growing toward a size that requires more than four billion addresses. Increasing the size of IP addresses required modifications to the layout of IP packets, which meant that all systems that handle IP packets—in other words, everything connected to the Internet—must be upgraded. To be on the safe side, the new system uses an address length of no less than 128 bits, allowing a mind-boggling number of addresses:

340,282,366,920,938,463,463,374,607,431,768,211,456

For unknown reasons, the existing Internet Protocol has version number four. Five was already taken by something else, so the new version got six; hence IPv4 and IPv6. In addition to the larger addresses, IPv6 differs from IPv4 in a number of aspects, so the IPv4 ways of doing things don't always translate one-to-one. But IPv6 is still IP, and it can fulfill the same functions as IPv4. Just on a much larger scale.

IPv6 by the end of 2012: 1 percent full or 99 percent empty?

2012 was a good year for IPv6. Netapp's Lars Eggert has been measuring how many of the top 500 websites have IPv6 enabled. After last year's World IPv6 Day and this year's World IPv6 Launch, we're now at around 10 percent for the top 500 sites in Finland, Germany, India, Japan, South Korea, the UK, and the US. China is lagging behind at 4.8 percent. And of the worldwide top 500 sites, 22.4 percent have an IPv6 address in the DNS, up from eight percent a year ago. However, of the Alexa top one million websites, only five percent have an IPv6 address in the DNS.

According to Google's measurements (Flash required), currently about one percent of its users is able to reach those IPv6-enabled websites over IPv6, up from 0.4 percent a year ago and 0.2 percent two years ago. So the rate at which Google's users are taking up IPv6 has increased from a factor two in 2011 to a factor 2.5 in 2012. If we can stick with that factor 2.5, the entire Internet will have IPv6 by the end of 2017. Of course, these types of growth tend to slow down as they approach 100 percent.

More evidence that IPv6 is taking off can be found in a paper on measuring the deployment of IPv6. Researchers at the Cooperative Association for Internet Data Analysis (CAIDA) observe that after years of linear growth, IPv6 deployment across the autonomous systems (mostly ISP networks) that make up the Internet started to go up along an exponential curve around 2008. The growth of IPv4 autonomous systems, on the other hand, had been exponential until about a decade ago. It's linear since. Note the slightly different scales in the figure, though: 40,000 IPv4 ASes versus 4500 IPv6 ASes.

Last but not least, there are actual IPv6 traffic statistics. Akamai's IPv6 statistics show the content network has 0.8 percent IPv6 hits in North America, 0.3 percent in Europe, and less than 0.1 percent elsewhere. The 0.3 percent number is similar to the amount of IPv6 traffic at two of Europe's big Internet Exchanges: AMS-IX in Amsterdam and DE-CIX in Frankfurt. AMS-IX IPv6 traffic has always been relatively high, but DE-CIX IPv6 traffic has increased from 1 to 5 Gbps in the past twelve months.