Which of the following best describes a unicast IPv6 address?

Fixed total of 128 bits, where 64 bits are used for routing and 64 bits are used as an interface identifier.

Fixed total of 128 bits, where 32 bits are used for the global prefix, 32 bits are used for the subnet and 64 bits are used as an interface identifier.

Variable total length, where at least 48 bits are used for the global prefix, 48 bits are used for the subnet and 64 bits are used as an interface identifier.

Variable total length, where at least 64 bits are used for routing and 64 bits are used as an interface identifier