1,370 million IPv4 addresses were used up this past decade. We have 722 million left, so the bottom of the pool is in sight.

There are 3,706,650,624 usable IPv4 addresses. On January 1, 2000, approximately 1,615 million (44 percent) were in use and 2,092 million were still available. Today, ten years later, 2,985 million addresses (81 percent) are in use, and 722 million are still free. In that time, the number of addresses used per year increased from 79 million in 2000 to 203 million in 2009. So it's a near certainty that before Barack Obama vacates the White House, we'll be out of IPv4 address. (Even if he doesn't get re-elected.)

The Internet Assigned Numbers Authority (IANA), part of the Internet Corporation for Names and Numbers (ICANN), manages the IPv4 address space. IANA delegates blocks of 16,777,216 addresses called "/8s" to the five Regional Internet Registries (AfriNIC, APNIC, ARIN, LACNIC and the RIPE NCC) which in turn give out address space to Internet Service Providers and (sometimes) end-user organizations. As of the end of 2008, IANA held 34 unused /8s and the RIRs together held 371.91 million unused addresses. The current status is:

Delegated to/status Blocks +/- 2009 Addresses



(millions) Used

(millions) Available



(millions) AfriNIC 2 33.55 14.89 18.66 APNIC 34 +4 570.43 540.36 30.06 ARIN 31 520.09 486.58 33.51 LACNIC 6 100.66 79.77 20.89 RIPE NCC 30 +4 503.32 450.11 53.21 RIRs subtotal 103 +8 1728.05 1571.71 156.34 Legacy 92 1543.50 1413.88 129.62 Unallocated 26 -8 436.21 436.21 Totals 221 3707.76 2985.59 722.17

So the IANA global pool was only reduced by 8 /8s, but the RIRs collectively reduced their working inventory by another 5 /8s, bringing the total reduction of the free address space 13 /8s, or 203.4 million IPv4 addresses, to be exact. This makes 2009 the first year since 1992 that the number of IPv4 addresses given out has been more than 200 million. Before 1993, the amount of address space given out was much larger because only class A (16.78 million addresses), class B (65,536 addresses), or class C (256 addresses) blocks could be given out. In 1993 the routing system was upgraded to Classless InterDomain Routing (CIDR), so it could work with address blocks that are an arbitrary power of two in size. (In CIDR notation, a /8 is a block of 2(32-8) = 16,777,216 addresses.)

There is an old story that Stanford University supposedly has more IPv4 addresses than the entire country of China. At the beginning of the decade, this was true: Stanford had the entire 36.0.0.0/8 class A block, more than twice the less-than 8 million addresses that were given out in China at the time. Times have changed, however. Last year, China passed Japan and took the number-two spot behind the US. This year, organizations in China obtained another 50.67 million addresses for a total of 232 million. And Stanford is one of the very few organizations that has returned a class A block. The top 15 IPv4-using countries are now:

Rank (was) Country January 1, 2010

(millions) January 1, 2009

(millions) Increase (percent) 1 United States 1495.13 1458.21 2 2 China 232.45 181.80 28 3 Japan 177.15 151.56 17 4 Europe general 149.48 120.29 24 5 (6) Germany 86.51 81.75 6 6 (9) Korea 77.77 66.82 16 7 Canada 76.96 74.49 3 8 France 75.54 68.04 11 9 (6) United Kingdom 74.18 86.31 -14 10 Australia 39.77 36.26 10 11 Brazil 33.95 29.75 14 12 Italy 33.50 29.64 13 13 (14) Russia 28.47 23.18 23 14 (13) Taiwan 27.10 24.01 13 15 (17) Netherlands 22.84 21.67 5

The reduction in address use by the UK is because net 51.0.0.0/8 is now registered as country "EU" rather than "GB". The US now holds a hair over 50 percent of all IPv4 address space given out (down from 52.4 percent a year ago), the other top 15 countries have 38 percent (up from 35.8 percent), and the rest of the world has 12 percent, up from 11.8.

So what does all of this mean for the future? For 2010, probably not much, but 2010 could be the last year for IPv4 as we know it. If IANA goes back to giving out 12 /8s to the RIRs per year, IANA will be giving out the fifth-to-last /8 somewhere in 2011 and then automatically also the other four. After this, it is unlikely that current IPv4 address assignment policies will remain in effect for much longer. This is in line with APNIC's Geoff Huston's automated predictions, which currently peg September 14, 2011 as the day the IANA global pool runs out, and November 1, 2012, as the day we last scrape the bottom of the IPv4 barrel. At that point, running an IPv4 network will start to look a lot like a big game of musical chairs.

The good news is that although a hundred thousand times more IPv6 than IPv4 space has been given out, 99.974 percent of it is still available. So after taking the IPv4-to-IPv6 transition hurdle somewhere between the next Olympics and the next presidential elections, the Internet has ample room to continue growing.