Ipv6 Interface ID

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identifies an IPv6 interface on a subnet and must be unique within that subnet. An IPv6 address is written such as the Classless Inter-Domain Routing (CIDR) notation in IPv4, for example the
1 64 128
Global Routing Prefix Subnet ID Interface ID
Figure 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.
Length of the prefix (global routing prefix + subnet IDentity) 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, whereas a valid IPv6 address be 2001:db8:72ed::417f:8c7f:f12d:96f7/64.
For all addresses, the interface ID has to be exactly 64 bits long which makes the differentiation between network- & host portion more easily since the boundary is every time the same. This stands in contrast to Internet Protocol version 4, by in which the size of the subnet could vary using the Variable Length Subnet Mask (VLSM) techniques. The interface IDentity is created with the Modified EUI-64 Format Interface Identifiers, which takes the 48 bit long MAC address of the Ethernet card and expands it to the 64 bits needed for the interface ID (RFC 4291, identifiable by the bytes ff:fe in the middle of the interface ID). This has the undesirable effect so that an interface will always have the same interface ID independent of what site it resides or what prefix it currently uses. This actually makes a node trackable, for example in the case of a mobile phone which accesses the ...

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...ecified address is 0:0:0:0:0:0:0:0, or simply:
IPv6 defines addresses for different scopes which are maintained by the IANA, [55]. “Every IPv6 address other than the unspecified address has a specific scope, which is a topological span within which the address may be used as a unique identifier for an interface or set of interfaces”, [39, p. 37]. Currently, there are two common scopes definied for unicast addresses: the link-local scope and the global scope, (RFC 4007). Addresses within the link-local scope are only for the usage on a single link, i.e., they are not routed. The allocated space is fe80::/10. If an IPv6 node has several interfaces, each of these interfaces has its own link-local address. Addresses within the global scope are unique IPv6 addresses inside the entire Internet. They are used for global communications. RFC 4193 further defines the unique

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