IPv6地址的类型是由地址的leading bits决定的。组成这些leading bits的变长域叫做Format Prefix (FP)。
001 (binary) 的FP是Aggregatable Global Unicast address。
Aggregatable addresses包括3级：
Public topology
site topology
interface identifier
Aggregatable global unicast address structure
如下：
| 3| 13 | 8 | 24 | 16 | 64 bits | +--+-----+---+--------+--------+--------------------------------+ |FP| TLA |RES| NLA | SLA | Interface ID | | | ID | | ID | ID | | +--+-----+---+--------+--------+--------------------------------+ <--Public Topology---> Site <--------> Topology <------Interface Identifier----->
FP，Format Prefix (001)
TLA ID，Top-Level Aggregation identifier
RES，保留给未来使用。
NLA ID，Next-Level Aggregation Identifier
SLA ID，Site-Level Aggregation Identifier
Next-Level Aggregation Identifier
组织可以创建字节的地址层级，如有自己的Site ID
| n | 24-n bits | 16 | 64 bits | +-----+--------------------+--------+-----------------+ |NLA1 | Site ID | SLA ID | Interface ID | +-----+--------------------+--------+-----------------+
如下，可以自由划分
| n | 24-n bits | 16 | 64 bits | +-----+--------------------+--------+-----------------+ |NLA1 | Site ID | SLA ID | Interface ID | +-----+--------------------+--------+-----------------+ | m | 24-n-m | 16 | 64 bits | +-----+--------------+--------+-----------------+ |NLA2 | Site ID | SLA ID | Interface ID | +-----+--------------+--------+-----------------+ | o |24-n-m-o| 16 | 64 bits | +-----+--------+--------+-----------------+ |NLA3 | Site ID| SLA ID | Interface ID | +-----+--------+--------+-----------------+
Site level aggregation ID
也可以类似划分
| n | 16-n | 64 bits | +-----+------------+-------------------------------------+ |SLA1 | Subnet | Interface ID | +-----+------------+-------------------------------------+ | m |16-n-m | 64 bits | +----+-------+-------------------------------------+ |SLA2|Subnet | Interface ID | +----+-------+-------------------------------------+
https://tools.ietf.org/html/rfc2374