The current system of managing Internet address space involves Regional Internet Registries (RIRs), which together share a global responsibility delegated to them by the Internet Assigned Numbers Authority (IANA). This regime is now well established, but it has evolved over ten years from a much simpler, centralized system. Internet number spaces were originally managed by a single individual authority, namely the late Jon Postel, co-inventor of some of the most important technical features of todays Internet.

It is important to understand that the evolution of the RIR system was not simply the result of Internet growth and the natural need to refine and decentralize a growing administrative task.

On the contrary, it arose from, and closely tracked, the technical evolution of the Internet Protocol, in particular the development of todays IP addressing and routing architecture.

In a relatively short time, the RIR system has evolved into a stable, robust environment for Internet address management. It is maintained today through self-regulatory practices that are well established elsewhere in the Internet and other industries, and it maintains its legitimacy and relevance by firmly adhering to open, transparent, and participatory decision-making processes.

Before the RIRs

IP Address Architecture

An important feature of the Internet Protocol (IP) is the ability to transparently use a wide variety of underlying network architectures to transport IP packets. This is achieved by encapsulating IP packets in whatever packet or frame structure the underlying network uses. Routers connecting different networks forward IP traffic by decapsulating incoming IP packets and then re-encapsulating them as appropriate for the next network to carry them.

To achieve this task with full transparency, the IP needed an addressing structure, which developed as a two-level hierarchy in both addressing and routing. One part of the address, the network part, identifies the particular network a host is connected to, while the other part, the local part, identifies the particular end-system on that network.

Internet routing, then, has to deal only with the network part of the address, routing the packet to a router directly connected to the destination network. The local part is not used at all in Internet routing itself; rather it is used to determine the intended address within the addressing structure of the destination network. The method by which the local part of an IP address is translated to a local network address depends on the architecture of the destination network static tables, simple conversions, or special purpose protocols are used as appropriate.

The original Internet addresses comprised 32 bits, the first eight bits providing the network part and the remaining 24 bits the local part. These addresses were used for a number of years. However, in June 1978, in IEN 46 A proposal for addressing and routing in the internet, Clark and Cohen observed:

The current internet header has space to name 256 networks. The assumption at least for the time being, is that any network entering the internet will be assigned one of these numbers. While it is not likely that a great number of large nets, such as the ARPANET, will join the internet, the trend toward local area networking suggests that a very large number of small networks can be expected in the internet in the not too distant future. We should thus begin to prepare for the day when there are more than 256 networks participating in the internet.

Classful addressing

As predicted, it soon became necessary to adapt the address architecture to allow more networks to be connected. By the time the Internet Protocol itself was comprehensively specified (in RFC 790, published in 1981, edited by Jon Postel), the IP address could be segmented in a number of ways to provide three classes of network address.

In class A, the high order bit is zero, the next seven bits are the network, and the last 24 bits are the local address. In class B, the high order two bits are one-zero, the next 14 bits are the network, and the last 16 bits are the local address. In class C, the high order three bits are one-one-zero, the next 21 bits are the network and the last eight bits are the local address.
This so-called “classful” architecture served the Internet for the next 12 years, during which time it grew from a small US-based research network to a global academic network showing the first signs of commercial development.

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