The Internet Assigned Numbers Authority (IANA) is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System (DNS), media types, and other Internet Protocol-related symbols and numbers. IANA is operated by the Internet Corporation for Assigned Names and Numbers, also known as ICANN.
Prior to the establishment of ICANN for this purpose, IANA was administered primarily by Jon Postel at the Information Sciences Institute of the University of Southern California, under a contract USC/ISI had with the United States Department of Defense, until ICANN was created to assume the responsibility under a United States Department of Commerce contract.
IANA is broadly responsible for the allocation of globally-unique names and numbers that are used in Internet protocols that are published as RFC documents. These documents describe methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems. IANA also maintains a close liaison with the Internet Engineering Task Force (IETF) and RFC Editorial team in fulfilling this function.
In the case of the two major Internet namespaces, namely IP addresses and domain names, extra administrative policy and delegation to subordinate administrations is required because of the multi-layered distributed use of these resources.
IANA delegates allocations of IP address blocks to regional Internet registries (RIRs). Each RIR allocates addresses for a different area of the world. Collectively the RIRs have created the Number Resource Organization formed as a body to represent their collective interests and ensure that policy statements are coordinated globally.
The RIRs divide their allocated address pools into smaller blocks and delegate them in their respective operating regions to Internet service providers and other organizations. Since the introduction of the CIDR system, IANA typically allocates address space in the size of /8 prefix blocks for IPv4 and /12 prefix blocks from the 2000::/3 IPv6 block to requesting regional registries as needed.
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