identifies an IPv6 interface on a subnet and must be unique within that subnet. An IPv6 address is written as CIDR (Classless Inter-Domain Routing) notation in IPv4, for example 1 64 128Global Routing Prefix Subnet ID Interface IDFigure 2.1. : IPv6 address format: the global routing prefix (n bits) identifies a site, the subnet ID (64 - n bits) a link within a site, and the interface ID (64 bits) a single IPv6 node. The prefix length (global routing prefix + subnet ID) is added after a slash to the IPv6 address: IPv6 address/prefix length. If we take an example, a valid IPv6 prefix is ​​2001:db8:72ed::/48, while a valid IPv6 address is 2001:db8:72ed::417f:8c7f:f12d:96f7/64. For all addresses, the interface ID must be exactly 64 bits, which makes it easier to differentiate between the network part and the host part since the limit is the same each time. This contrasts with Internet Protocol version 4, in which the subnet size could be varied using variable-length subnet mask (VLSM) techniques. The Interface IDentity is created with modified EUI-64 format interface identifiers, which take the 48-bit MAC address of the Ethernet card and extend it to the 64 bits needed for the interface ID ( RFC 4291, identifiable by the ff:fe bytes in the middle of the interface ID). This has the undesirable effect of an interface always having the same interface ID, regardless of which site it resides on or what prefix it is currently using. This actually makes a node trackable, for example in the case of a mobile phone accessing...... middle of paper...... the specified address is 0:0:0:0:0 :0:0:0, or simply :IPv6 defines addresses for different scopes which are maintained by IANA, [55]. “Each IPv6 address other than the unspecified address has a specific scope, which is a topological extent within which the address can be used as a unique identifier for an interface or set of interfaces,” [39, p. 37]. Currently, there are two common scopes defined for unicast addresses: link-local scope and global scope (RFC 4007). Addresses in the link-local scope are only intended for use on a single link, that is, they are not routed. The allocated space is fe80::/10. If an IPv6 node has multiple interfaces, each of these interfaces has its own link-local address. Global addresses are unique IPv6 addresses across the entire Internet. They are used for global communications. RFC 4193 further defines the unique