Aggregatable global addresses

Aggregatable global unicast addresses are equivalent to public IPv4 addresses. They are globally routable and reachable on the IPv6 portion of the Internet.

A global unicast address has the following format:

Global routing prefix: Used to identify a specific customer site. The size of the field is 48 bits and allows an ISP to create multiple levels of addressing hierarchy within the network to both organize addressing and routing for downstream ISPs and identify sites.
Subnet ID: Used by an individual organization to identify subnets within its site. The organization can use these 16 bits to create 65536 subnets or multiple levels of addressing hierarchy.
Interface ID: Indicates the interface on a specific subnet. The size of this field is 64 bits.

Figure 1. Global unicast address format

First 3 bits are 001, next 45 bits are global routing prefix, next 16 bits are subnet ID, last 64 bits are interface ID