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How IP addresses get distributed

This chart illustrates the way Internet Protocol address numbers are distributed by gatekeepers such as the Internet Corporation for Assigned Names and Numbers.

IP addresses are unique numbers that map computers across the Internet. Obtaining them has become a high priority for service providers and large organizations. Here's a look at the gatekeepers who oversee how the numbers are handed out.

Chain of power
Below are the organizations responsible for distributing IP address numbers.

Internet Corporation for Assigned Names and Numbers (ICANN)
Based on a 1998 agreement with the Commerce Department, ICANN oversees the Internet Assigned Numbers Authority (IANA) and controls how the Net's 4.29 billion IP addresses are used.
Under ICANN, IANA distributes address space to three geographically diverse Regional Internet Registries (RIRs) and is supposed to encourage all three RIRs to operate so that addresses remain unique, are mapped efficiently, and are treated as a precious resource.

Regional Internet Registries (RIR)
Three nonprofit registries dole out available pools of IP based on a shared criteria. All deploy numerical address space to ISPs, local registries, and in some cases small users.

RIR worldwide breakdown
American Registry for Internet Numbers (ARIN)
Hands out number blocks to thousands of major ISPs such as WorldCom, UUNet, Sprint, and other large users of IP addresses, such as corporations and colleges. Many of ARIN's customers then pass the numbers on to smaller ISPs or end users.
Réseaux IP Européens (RIPE)
This registry allocates IP numbers for all of Europe and gives out number blocks to any ISP no matter the size.
Asia Pacific Network Information Centre (APNIC)
Like ARIN it encourages smaller ISPs to go upstream and get IP numbers from bigger providers. Large members include: Japan and Korea Network Information Centers, China Telecom, and China Education and Research Network.
Sources: ARIN, ICANN, Tony Rutkowski