00::/3 Reserved by IETF Unique Local Unicast (0.78%) 6000::/3 Reserved by IETF 8000::/3 Reserved by IETF Other defined uses (0.39%) A000::/3 Reserved by IETF C000::/3 Reserved by IETF E000::/4 Reserved by IETF Multicast (0.39%) F000::/5 Reserved by IETF F800::/6 Reserved by IETF 85.84% FC00::/7 Unique Local Unicast Link Local Unicast (0.10%) FEOO::/9 Reserved by IETF FE80::/10 Link Local Unicast FECO::/10 Reserved by IETF FF00::/8 Multicast Figure 3.6 Usage of IPv6 address space as of January 2013. Introduction to IPv6 IPv4-compatible IPv6 address: 80 bits 16 bits 32 bits 00000 IPv4 address IPv4-mapped IPv6 address: 80 bits 16 bits 32 bits 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 F F F IPv4 address IPv4-embedded IPv6 address (one of the six defined in RFC 6052): 96 bits 32 bits Prefix used for IPv4/IPv6 protocol translation IPv4 address Teredo address format: 32 bits 32 bits 16 bits 16 bits 32 bits Prefix Server IPv4 address Flags UDP Port Client IPv4 address Figure 3.7 Examples of IPv4 addresses embedded within IPv6 addresses. utilize inclusion of IPv4 addresses within IPv6 addresses (see more about transition mechanisms in Section 5.3, and in particular IPv4-Embedded IPv6 address format in Figure 5.3). Examples of such address uses include, but by no means are limited to, the following examples and the illustration in Figure 3.7: IPv4-compatible IPv6 address: This deprecated address format was designed to help in IPv6 transition. IPv4-mapped IPv6 address: This address format is to represent IPv4 addresses as IPv6 addresses. The format is used, for example, to simplify Application Programming Inter- faces (APIs) by allowing both address families to be presented by the same fields, parameters, and variables. IPv4-embedded IPv6 address: Six IPv4-embedded address formats have been defined for IPv4/IPv6 Network Address Translation (NAT64) use in RFC 6052 [13]. Figure 3.7 illustrates the simplest of these formats. For more details of possible NAT64 address formats please refer to Section 5.3.3. Teredo address: The Teredo 