IPv6 Routing Prefix
IPv4 addresses are 32 bits long, whereas IPv6 addresses are 128 bits. IPv6
addresses are composed of the following elements (see Figure 8-1):
�¡ The first three bits (/3) of unicast always 001.
�¡ The next 13 bits (/16) are Top-Level Aggregator (TLA) the upstream
ISP.
�¡ The next 24 bits (/40) are the next-level aggregator or regional ISP.
�¡ Enterprises are assigned /48 and have 16 bits of subnetting.
Figure 8-1 RFC 2374 IPv6 Address Structure
Format
3b
Site-Level Aggregation
16b
Next-Level
Aggregation
24b
Rsvd8b Top-Level
Aggregation
13b
Interface ID