The IPv6 transition mechanisms include a technique for hosts and routers to tunnel IPv6 packets dynamically under IPv4 routing infrastructure. IPv6 nodes that utilize this technique are assigned special IPv6 unicast addresses that carry an IPv4 address in the low-order 32 bits. This type of address is called an IPv4-compatible IPv6 address. The address format is shown in the following table.
Table 1–5 IPv4–Compatible IPv6 Address Format
80 bits |
16 bits |
32 bits |
0000.......................................0000 |
0000 |
IPv4 Address |
A second type of IPv6 address that holds an embedded IPv4 address is also defined. This address is used to represent an IPv4 address within the IPv6 address space. This address is mainly used internally within the implementation of applications, APIs, and the operating system. This type of address is called an IPv4-mapped IPv6 address. The address format is shown in the following table.
Table 1–6 IPv4–Mapped IPv6 Address Format
80 bits |
16 bits |
32 bits |
0000..............................0000 |
FFFF |
IPv4 Address |