Address block

The address space of IPv6 is divided into 8 blocks (/3)
3 bits is not friendly to hexadecimal
Let's consider /4 (i.e. 16 blocks)

The first hexadecimal figure:
0, 1   Special (e.g loopback)
2, 3   Aggregatable global
4, 5   Not assigned
6, 7   Not assigned
8, 9   Not assigned
a, b   Not assigned
c, d   Not assigned
e, f   Link-local, site-local, multicast