IPv6 Addresses With Embedded IPv4 Addresses

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