The IPv6 Global Unicast Address Space is the equivalent of the assignable IPv4 address space.
Address blocks are handed out to the Regional Internet Registries, which in turn hand smaller blocks to Internet Service Providers (ISPs). ISPs then hand out addresses to end users. The first three bits of the global unicast address space are 001, indicating that any address using this prefix always begins with the number 2 or 3 (0010 or 0011). The following table is adapted from RFC 3587.
|Prefix||Global Routing Prefix||Subnet ID||Interface ID|
|3 bits||45 bits||16 bits||64 bits|