And indeed, they have been running out for the past ten years - look at slide 5 from this presentation: https://www.arin.net/knowledge/v4_deplete_v6_adopt.pdf The fact is that ISPs and hosting companies are having to now undergo major changes in order to continue to grow. The fact that we've known this was coming and developed IPv6, gotten into every major OS and the gear of every major network equipment manufacturer is simply good preparation for what's to come.

In this stage, APNIC has a fixed block of address space reserved and available under a special policy for new and emerging service providers, but that doesn't help one much if you're a existing telecomm company who had been getting tens of thousands of addresses every few months in order to grow - you can now longer obtain additional blocks and now must scramble to come up with an alternative (such as IPv6) if you want to keep growing. More info - http://www.apnic.net/community/ipv4-exhaustion/exhaustion-and-network-operators

There is a finite number of IPv4 address (2**32, aka approx 4.3 billion)... There are 7 billion people on the planet today, and most want an always on smartphone, and a home computer, and a computer at work, etc. This doesn't consider the demand for office servers, data centers, cloud services, etc. The reality is that the depletion of the free pool doesn't mean we run out, but it does start us on the path of higher and higher utilization of these 4.3B numbers. At some point, it becomes very difficult to get additional addresses because all of the relatively easily recovered address space has been redeployed. For an ISP, this won't be 2012, but there's no assurance that its not going to happen very quickly in the next few years.

It's worth reading the original article referenced in the post... The central free pool of IPv4 address space ran out on 3 February 2011. The Asia Pacific region (under the APNIC registry) ran out of address space for issuance per their standard policies at the start of summer. RIPE (serving Europe) is likely to run out in this spring, and ARIN is likely to run out in early 2013. Telecommunication companies and ISPs rely on getting additional address space from their regional registry, and if they can't get any more IPv4 space, they either need to stop adding new customers, scavenge IPv4 space from elsewhere, or use IPv6 for new customers.

Registrations are publicly visible in the WHOIS database, so please elaborate which address blocks you refer to?

Only parties with operational need can obtain address space, whether that's directly from the Internet number registries or via transfer from an existing address holder.

Correct.  If you received IPv4 address space directly from one of the Internet number registries (whether that was IANA, or the InterNIC, or a regional Internet registry), the address space is assigned to you and can be transferred to another party according to the policies of the registry serving your region.  If you received address space from your ISP, it's quite likely that the ISP is only providing it to you as a component of service and will recover them if you leave or change providers.

( Here's an example of lessons learned - this message from Facebook Engineering http://www.facebook.com/note.php?note_id=10150198443513920 )

World IPv6 Day came to an end earlier today. We successfully enabled IPv6 on our site for 24 hours, with great results. We saw over 1 million users reach us over IPv6.

We’re pleased that we did not see any increase in the number of users seeking help from our Help Center. The estimated 0.03% of users who may have been affected would have experienced slow page loads during the test.

Based on the encouraging results, we’ve decided to leave our Developer site dual-stacked, supporting both IPv4 and IPv6. And we will continue to adapt our entire code base and tools to support IPv6.

We are glad to have joined with the Internet Society, major Web companies, and other industry players to enable IPv6 for this test day. It was a great opportunity to test our infrastructure and IPv6 readiness.

IPv6 is vital to the continued growth of the Internet, and World IPv6 Day was a great step in the advancement of the protocol.  We hope the overall success of the 24 hour test will encourage others in the industry to establish reliable IPv6 connectivity and develop robust IPv6 products.

Sase - anyone may submit proposals to change ARIN's policies... Go to www.arin.net/policy for details on doing so.

7 Billion people on the planet... While many today do not have Internet connectivity, that's changing rapidly where some regions are skipping the copper deployment for end users and going directly to deployment of wireless infrastructure. In more established economies, it is not uncommon to have 1 IP address in use at home for broadband, one in the office, one on your mobile device, etc. 4 or 5 IP's per person, 7 Billion people = 40 or 50 Bill IP addresses would be helpful, and this doesn't even count servers in data centers, virtual machines, clouds, etc. 4.3 billion is looking very tight even with just today's applications.

Incorrect. Blocks allocated prior to ARIN are still maintained in the ARIN database accordingly to community policies. This includes processing contract, updates, being reclaimed, etc.
/John
John Curran President and CEO
ARIN

If it''s registered in the ARIN service region, then its subject to policies developed by the community in this region for transfers. Go to www.arin.net and click on "Got IPv4 Addresses" for details.
Thanks!
/John

John Curran
President and CEO
ARIN

The fact that I said it doesn't make it true, but I definitely believe that there will be many organizations running IPv4 internally for years to come, and it's only when its commonplace to use IPv6 will organizations think about turning off IPv4. Your mileage may vary.
/John
President and CEO, ARIN

Steveb - No supreme dictator, but there is an ARIN policy process and *anyone* in the community can submit proposals... https://www.arin.net/policy/pdp.html

Slight difference... ISPs can still get (today) fresh blocks of IPv4 addresses. That *will* end in about one year, and then you'll see layers of NAT as you've never seen them before...