Regional Internet Registries (RIR) are responsible for managing network resources for IP computer networks -- such as Internet Service Providers -- within their geographical region. The regions they cover, and the IP network resources they manage, are assigned by IANA (Internet Assigned Numbers Authority); an agency that is also responsible for managing the DNS root zone and for generally assigning numbers for the Internet. IANA was headed by Jon Postel in the 1970s and 1980s, and evolved from the ARPANET computer network project. The ARPANET computer network was one of the first to expand to include International nodes -- the first nodes (locations) were located in Norway and England (London) -- and it became obvious that organisations would need to be created to manage network resources, such as host tables and network numbers. Therefore, the need for Regional Internet Registries (RIR) evolved from ARPANET and a need to manage International network resources.
APRPANET was an American research project, and IANA were/are based in California; while IANA was capable of managing international nodes for ARPANET -- a far smaller network than the Internet, that connected military and academic institutions -- it soon became apparent it would not be capable of managing a growing Internet in the late 1980's. With its base in California, IANA lacked the regional knowledge and language skills to deal efficiently with international nodes. Réseaux IP Européens (RIPE) was the first Regional Internet Registries (RIR) created -- when TCP/IP eventually proved victorious in the protocol wars of the 1970s/1980s -- and initially managed network resources for European IP computer networks, such as: BelWue, HEPnet, CERN, EASInet, NORDUnet, EUnet, GARR, SWITCH, SURFnet and XLINK. As the Internet expanded, RIPE's responsibilities also expanded, and they now manage IP network resources for the Middle East and parts of Central Asia. There is now five Regional Internet Registries (RIR) to manage regional Internet names and numbers resources: RIPE NCC, LACNIC, APNIC, ARIN and AfriNIC.
So, what Internet resources does IANA delegate to Regional Internet Registries (RIR)? the most obvious Internet resource is the management of IP addresses. The first version of the Internet Protocol (IP) is version 4, a 32 character numerical label, which has a total of 4.3 billion numerical labels. IPv4 number blocks are now in short supply, and need careful management by RIRs. Alongside managing IPv4 resources, Regional Internet Registries (RIR) also manage: IPv6 resources, AS numbers (ASN), and Domain Name System (DNS) resources. DNS is a naming system for IP addresses, and RIRs manage DNS resources, such as: reverse DNS zones and authoritative name servers; RIPE manages the DNS root nameserver k.root-servers.net (one of thirteen root nameservers); the e164.arpa (ENUM) zone; and DNSSEC security for the Domain Name System (DNS).
The current five Regional Internet Registries (RIRs), who also form the Number Resource Organization, are: