Quality of Service and performance characterization of IPv6 relative to IPv4

II.4.7 IPv6 addresses with embedded IPv4 addresses

In environments where IPv4 and IPv6 nodes are mixed, another convenient form of IPv6 address notation is to put the values of an IPv4 address into the four low-order byte pieces of the address.

Because the transition to IPv6 will be gradual, two special types of addresses have been defined for backward compatibility with IPv4.^19(*)

II.4.7.1 IPv4-mapped IPv6 address

IPv4 mapped IPv6 addresses constitute a special class of IPv6 addresses. It allows a host that support both IPv4 and IPv6 to communicate with a host that supports only IPv4. The IPv6 address is based completely on the IPv4 address. This is an IPv6 that is used to represent an IPv4 address.

II.4.7.1.1 Notation

As a special exception to IPv6 addresses notation, IPv4 mapped addresses are commonly represented with their last 32 bits noted as an IPv4 address.

An IPv6 address has its first 80 bits set to zero, followed by 16 bits set to one, while its last 32 bits represents an IPv4 address.^20(*)

An example of IPv4-mapped IPv6 address

· 0:0:0:0:0:0.192.168.30.1 = ::192.168.30.1 is the same address as C0A8:1E01

II.4.7.2 IPv4-compatible IPv6 address

An IPv4 compatible address allows a host supporting IPv6 to talk IPv6 even if the local router(s) don't talk IPv6. IPv4 compatible address is used to tunnel IPv6 packets dynamically over an IPv4 routing infrastructure. It tells endpoint software to create a tunnel by encapsulating the IPv6 packet in an IPv4 packet.

II.4.7.2.1 Notation

80 bits of 0s followed by 16 bits of 0s, followed by a 32 bit IPv4 Address:

* ¹⁹ IPv6 essentials, O'REILLY, ISBN: 0-596-00125-8, page 31

* ²⁰ http://en.wikipedia.org/wiki/IPv4_mapped_address (May 13, 2006)