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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 4 (IP, IPv4)                      9  IP Addressing                           9  IP Addressing Concepts and Issues

Number of IP Addresses and Multihoming 1 2 IP "Classful" (Conventional) Addressing

The Original IP Address Authority: IANA

The Internet is of course “the” big IP internetwork, and requires this coordination task to be performed for millions of organizations worldwide. The job of managing IP address assignment on the Internet was originally carried out by a single organization: the Internet Assigned Number Authority (IANA). IANA was responsible for allocating IP addresses, along with other important centralized coordination functions such as managing universal parameters used for TCP/IP protocols. In the late 1990s, a new organization called the Internet Corporation for Assigned Names and Numbers (ICANN) was created. ICANN now oversees the IP address assignment task of IANA, as well as managing other tasks such as DNS name registration.

IP addresses were originally allocated directly to organizations. The original IP addressing scheme was based on classes, and so IANA would assign addresses in Class A, Class B and Class C blocks. Today, addressing is classless, using CIDR’s hierarchical addressing scheme. IANA doesn’t assign addresses directly, but rather delegates them to regional Internet registries (RIRs). These are APNIC, ARIN, LACNIC, and RIPE NCC. Each RIR can in turn delegate blocks of addresses to lower-level registries such as national Internet registries (NIRs) and local Internet registries (LIRs).

Eventually, blocks of addresses are obtained by Internet Service Providers (ISPs) for distribution to end-user organizations. Some of the ISP’s customers are “end-user” organizations, but others are (smaller) ISPs themselves. They can in turn use or “delegate” the addresses in their blocks. This can continue for several stages in a hierarchical fashion. This arrangement helps ensure that IP addresses are assigned and used in the most efficient manner possible. See the section on CIDR for more information on how this works.

IANA, ICANN and the RIRs are responsible for more than just IP address allocation, though I have concentrated on IP addresses here for obvious reasons. For more general information on IANA, ICANN, APNIC, ARIN, LACNIC and RIPE NCC, try a can of alphabet soup… or the topic on Internet registration authorities. J

Number of IP Addresses and Multihoming 1 2 IP "Classful" (Conventional) Addressing