Explanation/Reference:
Explanation:
Basic IPv6 Address Format

Image: The figure shows the three parts of an IPv6 address, which are described in the next text. The
leftmost three fields (48 bits) contain the site prefix. The prefix describes the public topology that is usually
allocated to your site by an ISP or Regional Internet Registry (RIR). The next field is the 16-bit subnet ID,
which you (or another administrator) allocate for your site. The subnet ID describes the private topology,
also known as the site topology, because it is internal to your site.
The rightmost four fields (64 bits) contain the interface ID, also referred to as a token. The interface ID is
either automatically configured from the interface's MAC address or manually configured in EUI-64 format.
Reference: http://docs.oracle.com/cd/E23823_01/html/816-4554/ipv6-overview-10.html