IPv6のアドレス体系（アドレスモデル）

   IPv6 Addresses of all types are assigned to interfaces, not nodes.
   Since each interface belongs to a single node, any of that node's
   interfaces' unicast addresses may be used as an identifier for the
   node.

   An IPv6 unicast address refers to a single interface.  A single
   interface may be assigned multiple IPv6 addresses of any type
   (unicast, anycast, and multicast).  There are two exceptions to this
   model.  These are:

     1) A single address may be assigned to multiple physical interfaces
        if the implementation treats the multiple physical interfaces as
        one interface when presenting it to the internet layer.  This is
        useful for load-sharing over multiple physical interfaces.

     2) Routers may have unnumbered interfaces (i.e., no IPv6 address
        assigned to the interface) on point-to-point links to eliminate
        the necessity to manually configure and advertise the addresses.
        Addresses are not needed for point-to-point interfaces on
        routers if those interfaces are not to be used as the origins or
        destinations of any IPv6 datagrams.

   IPv6 continues the IPv4 model that a subnet is associated with one
   link.  Multiple subnets may be assigned to the same link.