Figure 1-1 shows the format of unicast addresses. An interface ID identifies an interface on a link. The interface ID is required to be unique on a link, but it may also be unique over a broader scope. In many cases, the interface ID is derived from its Link layer address. The same interface ID can be used on multiple interfaces on a single node.
Unspecified address Indicates the absence of an address and is never assigned to an interface.
Loopback address Used by a node to send IP datagrams to itself and is typically assigned to the loopback interface. The IPv4 address is carried in the low-order 32 bits. IPv4-mapped IPv6 address Used to represent an IPv4 address and to identify nodes that do not support IPv6. This address is not used in an IPv6 packet. Do not advertise or propagate routes containing site-local prefixes outside the site.