Feb. 3, 2011 is a date that will live in infamy -- for some of us, anyway. That day marked the last time IANA will allocate a fresh /8 netblock to one of the Regional Internet Registries (ARIN, RIPE, and so on).
One could legitimately say that the Internet is indeed out of IPv4 addresses right now, but the pain won't really be felt until the RIRs deplete their allocations and ISPs burn through what they've already been allocated. That date will vary depending upon what part of the world you live in. The Asia-Pacific region is slated to run out first, but everyone else is close behind. Getting a good old dotted-quad IPv4 allocation from your ISP is going to be a fun bedtime story you can tell your kids within the next year or two.
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Introducing IPv6
Of course, as most technologies become overwhelmed by their own success, there's usually a replacement around the corner that's ready to jump in and save the day. In this case, that replacement is the much seen but rarely understood IPv6, and it's been around since 1998. Talk about a slow walk into the spotlight.
Replacing IPv4's theoretical maximum of about 4 billion addresses with about -- wait for it -- 340 trillion trillion trillion addresses, IPv6 will handily solve the address consumption problem. In case you're having a tough time wrapping your mind around the number, that's enough to give each human cell in your body an IPv6 address and still have some left for all of 34 trillion trillion other people's cells. It's safe to say the IETF working group that settled on a 128-bit address wanted to be fairly certain that we'd never have to go through this again.
Increasing the address space is by no means all that IPv6 does. IPv6 implements a raft of other changes over IPv4, including significantly more flexible multicast support, the elimination of broadcast (now just a type of multicast), autoconfiguration and renumbering support (with or without DHCP), a redesigned header and header extension mechanism, and a very sane hierarchal address format -- to name a few.
All of that is very cool, but it's also a fairly significant departure from what most of us are used to. Perhaps because of that variation, combined with generalized apathy, uptake of IPv6 among the Internet community has been extremely sluggish. As of this writing, only 8 percent of the active ASNs on the Internet are actually advertising routes to IPv6 networks, and a large portion of these are ISPs that form the backbone of the Internet. Only about 1.4 million DNS domain names include IPv6 AAAA name records (out of the 200 million-plus that exist). However, with the impending exhaustion of IPv4 address space, the transition will accelerate -- quickly.