 root zone management, and other numerical assignments, such as protocol and port numbers. (DNS, top-level domains, and root servers are all discussed later in this chapter.) In its role of administering the data in the root name servers (at the top of the DNS hierarchy), IANA works closely with top-level domain (TLD) and root name server operators, as well as those involved with policy decisions at ICANN. The registration of IP addresses around the world is delegated to five regional Internet registries (RIRs), which as a group are called the Number Resource Orga- nization (NRO; www.nro.net): American Registry for Internet Numbers (ARIN; www.arin.net) for North America Asia Pacific Network Information Centre (APNIC; www.apnic.org) for the Asia-Pacific region Reseaux IP European Network Coordination Center (RIPE NCC; www.ripe. net) for Europe, Central Asia, and the Middle East Latin American and Caribbean Internet Addresses Registry (LACNIC; www.lacnic.net/en) for Latin America and the Caribbean African Network Information Centre (AfriNIC; www.afrinic.net) for Africa Each RIR is responsible for overseeing the allocation and registration of Internet number resources within its region of the world. The resources the RIRs manage include both IPv4 and IPv6 addresses and autonomous system numbers. (Autono- mous systems are discussed later in this chapter.) IANA delegates large groups of IPv4 addresses to the various RIRs, which then reallocate smaller groups of addresses in their regions to ISPs and other organizations. A process has also been established for the allocation of IPv6 addresses, although at this time there is little pressure in this area as the supply of IPv6 addresses greatly exceeds the demand. The NRO has entered into an agreement with ICANN to establish an organization, referred to as the Address Supporting Organization (ASO; www.aso.icann.org) to deal with the coordination of global IP addressing policies within the ICANN framework. Since the formation of ICANN, the relationship between ICANN, the c