Backbone and number resource management hierarchy

Internet backbone network

The Internet backbone is the high-capacity core of the Internet: the principal fibre routes (terrestrial and submarine) and the powerful core routers operated by Tier-1 and large Tier-2 ISPs. It interconnects regional and national networks at IXPs and through private peering, carries long-distance traffic at 100 Gbps and above, and uses BGP to exchange routes between autonomous systems.

Hierarchy for management of Internet number resources

Number resources are IP addresses (IPv4/IPv6) and Autonomous System Numbers (ASNs). They are managed in a top-down hierarchy so that every address is unique worldwide and can be aggregated for routing.

              IANA  (global pool, under ICANN)
                |
   +------+-----+-----+------+
 AFRINIC APNIC ARIN LACNIC RIPE NCC   <- 5 RIRs
            |
          NIRs   (e.g. JPNIC, CNNIC, KRNIC, TWNIC)
            |
        LIRs = ISPs / large organisations
            |
        End users (customers)

1. IANA: holds the unallocated global pool. It allocates large blocks (IPv4 /8, IPv6 /12) and ASN ranges to the Regional Internet Registries according to global policy. The IANA IPv4 pool was exhausted in February 2011.
2. RIRs: five registries, each for one region (AFRINIC for Africa, APNIC for Asia-Pacific, ARIN for North America, LACNIC for Latin America and Caribbean, RIPE NCC for Europe, Middle East and Central Asia). They allocate to NIRs and LIRs, keep the WHOIS database and run policy development through open community processes.
3. NIRs (National Internet Registries): exist in some countries, e.g. Japan, China, Korea, Taiwan, India (IRINN). They serve ISPs in their country on behalf of the RIR.
4. LIRs (Local Internet Registries): usually ISPs, which receive blocks (e.g. IPv6 /32) from the RIR or NIR and assign smaller blocks to customers (e.g. IPv6 /48 per site, or a single IPv4 /24).
5. End users: organisations and individuals who use the assigned addresses.

In Nepal there is no NIR, so Nepali ISPs obtain IP blocks and ASNs directly from APNIC as members. The hierarchy supports aggregation, because each ISP's customers fall under one prefix, which keeps the global routing table small.