ARIN, the resource registry for IPv4 addresses in America, has announced that it has run out of IPv4 addresses to allocate. As a result, obtaining an IPv4 address in Americas has become much more difficult (although not impossible).
ARIN is one of five Regional Internet Registries that allocate IPv4 addresses to companies. These were fed blocks of addresses from IANA, the global registry of IPv4 addresses. The last blocks from IANA were distributed to the five RIRs in January 2011 which they have been using up since then. China ran out of IPv4 addresses some time ago, and many are nearing total exhaustion.
There are still IPv4 addresses that are effectively unused; some large organisations (such as Apple) have entire subnets allocated to them (17.x.x.x is an Apple IPv4 address). Although they could theoretically returns ome of these to the pool, IPv4 addresses are a fundamentally limited address space and this would add months to the lifespan of IPv4 addresses rather than decades. A 2006 XKCD comic shows the allocations at the time; in the past decade, this grid has become completely filled.
Enter IPv6
The solution, rather than haggling over final IPv4 addresses (the price of which will rise as a result of this), is to switch to IPv6. Networking technologists have been saying that IPv6 will be here in the next few years for most of the last couple of decades; in actual fact, it's used quite heavily already in places like AWS and for some backbone traffic over the internet. What's changed is the perception of the wider audience; enabling IPv6 is now not only possible, but practical.
Most operating systems (including mobile operating systems) have had IPv6 for years. Devices have run in dual-stack mode; they support both an IPv6 and IPv4 connection. For World IPv6 day in June 2011, big sites like Google, Facebook and Twitter publicly enabled IPv6 addresses for their back-end services. The majority of traffic saw no problems in being dual-stack enabled; and shortly afterwards, IPv6 was kept on for many large sites instead of rolling back to an IPv4 address space.
At the time, browsers would either prefer an IPv4 address instead of IPv6 (when both were available) due to the abundance of IPv4 websites (and corresponding lack of IPv6 sites). Since then, browsers and operating systems have taken a first-to-respond approach; by making simultaneous connections to both IPv4 and IPv6 and then continuing to use whichever responds fastest, the use of IPv6 has increased.
The recent release of iOS9 has also brought forward IPv6 connectivity; by requiring all apps to be IPv6 enabled, iOS9 for the first time can be run in IPv6 only. This also included documentation for how to test for IPv6 services on iOS devices. Because of an improved Happy Eyeballs algorithm, if an iOS9 device discovers an IPv6 address it will try and connect immediately; if an IPv4 address is discovered it waits up to 25ms to see if there's a corresponding IPv6 address to select between instead. This has the result of biasing connections towards IPv6 for dual-stack networks.
Meanwhile, In the UK, Sky have enabled a million end users with IPv6 bringing them to the 15th biggest IPv6 network. Meanwhile BT are expecting to have 50% of BT users by April 2016, with a transition to 100% coverage by December 2016 for those that have Home Hub 5 or newer. Outside the UK, Germany, Greece, USA, Peru, Swittzerland and Belgium all have over 10% of users on IPv6. Google reports that over the last month, global averages have been around 7-8% with USA penetration of around 20%. With the increase of iOS9 and OSX El Capitan preferring IPv6 by default, 2015 will be the year that global averages top 10%, although it will be awhile befpre IPv4 fades away.