IPv6 addressing architecture (1)

Global address: 2000::/3 (RFC3513/3587)
Hierarchy design to encourage route aggregation

Interface ID to help autoconfiguration (later)
Unique and stable number - pseudorandom, MAC address or something alike

Site boundary is fixed to /48 to encourage ISP change and site-local routing
A site can always have 2^16 subnets

Current RIR/ISP practice
Large ISP gets /32 from RIR (like 2001:200::/32)
Smaller ISP gets /40 suballocation from upstream ISP
End site (universities, companies) gets /48

| 3|       45         |   16   |          64 bits               |
+--+------------------+--------+--------------------------------+
|FP|                  |  SLA   |         Interface ID           |
|  |                  |  ID    |                                |
+--+------------------+--------+--------------------------------+
<--><-----------------><------->
giant managed by RIR   site subnet