Structure of Unicast Addresses

summarizable (=aggregable) global unicast addresses → enable more efficient routing infrastructure
Validity range of an IP address = the range in which it is unique (here global, Internet)
Format prefix (FP, 3 bit) managed by IANA
TLAs (Toplevel Aggregator, 13 Bit) are assigned by IANA to local Internet registrars, who in turn assign individual TLAs to large Internet providers.
8 bits reserved for future extensions
NLA (Next-Level-Aggregator, 24 Bit) identifies a certain customer location, with NLAs an Internet provider can design an addressing hierarchy with several levels within a network.
SLA (Site Level Aggregator, 16 Bit) that organizes addressing and routing for downstream Internet providers and identifies sites or subnets within a site.
Interface ID (64 bit) identifies the interface within the subnet, is either derived from the 48 bit MAC address of the NIC or can be generated randomly.

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