at Figure 3.1 shows how a 128-bit IPv6 address is generally formatted, as of today. The first three bits have special meaning for addresses: the 000 indicates no constraint on the Interface IDentifier (IID) structure, 001 indicates currently assigned global prefixes, and 111 is for other addresses such as multicast. As it is visible from the current allocation of the first three bits, the main part of the IPv6 address space remains reserved for the future. This significant reservation allows totally different addressing schemes to be invented, and hence helps in creation of backwards compatible extensions. An IPv6 address is split into three different sections: a global prefix, a subnet identifier, and an IID. The global prefix refers to a prefix that a network has obtained for its use. These prefixes typically range from 32-bits to 56-bits (/32 to /56), but any other length is of course possible. The subnet identifier includes the bits after global prefix that are used within a network to identify a subnet, which is typically a link. The final bits hold an IID, which identifies a particular network interface (typically a host), inside the subnet. 128 bits n bits m bits 128 - n - m bits global prefix subnet ID Interface Identifier (IID) First upper three (3) bits have special meaning for global unicast addresses: 000: no constraint on the IID structure 001: currently assigned global prefixes : unassigned 111: other addresses like multicast etc. Figure 3.1 Generic IPv6 address architecture. Introduction to IPv6 3.1.2 IPv6 Address Types An IPv6 address can be of three different types: unicast, anycast, or multicast. The unicast type of address identifies a single network interface in a single node. The anycast address type identifies the set of interfaces typically on different nodes. An IPv6 packet sent to an anycast address is delivered by the routing system to the nearest instance of an anycast address. The multicast type of address identifies a multitude of interfaces on, usually, a multitude of hosts. An IPv6 