RFC 4291 – IPv6 Addressing Architecture

http://www.ietf.org/rfc/rfc4291.txt

Interesting things to remember:

   IPv6 addresses are 128-bit identifiers for interfaces and sets of
   interfaces (where "interface" is as defined in Section 2 of [IPV6]).
   There are three types of addresses:

    Unicast:   An identifier for a single interface.  A packet sent to a
               unicast address is delivered to the interface identified
               by that address.
    Anycast:   An identifier for a set of interfaces (typically
               belonging to different nodes).  A packet sent to an
               anycast address is delivered to one of the interfaces
               identified by that address (the "nearest" one, according
               to the routing protocols' measure of distance).
    Multicast: An identifier for a set of interfaces (typically
               belonging to different nodes).  A packet sent to a
               multicast address is delivered to all interfaces
               identified by that address.

   There are no broadcast addresses in IPv6, their function being
   superseded by multicast addresses.
---
2.5.5.1.  IPv4-Compatible IPv6 Address

   The "IPv4-Compatible IPv6 address" was defined to assist in the IPv6
   transition.  The format of the "IPv4-Compatible IPv6 address" is as
   follows:
   |                80 bits               | 16 |      32 bits        |
   +--------------------------------------+--------------------------+
   |0000..............................0000|0000|    IPv4 address     |
   +--------------------------------------+----+---------------------+

   Note: The IPv4 address used in the "IPv4-Compatible IPv6 address"
   must be a globally-unique IPv4 unicast address.

   The "IPv4-Compatible IPv6 address" is now deprecated because the
   current IPv6 transition mechanisms no longer use these addresses.
   New or updated implementations are not required to support this
   address type.

2.5.5.2.  IPv4-Mapped IPv6 Address

   A second type of IPv6 address that holds an embedded IPv4 address is
   defined.  This address type is used to represent the addresses of
   IPv4 nodes as IPv6 addresses.  The format of the "IPv4-mapped IPv6
   address" is as follows:
   |                80 bits               | 16 |      32 bits        |
   +--------------------------------------+--------------------------+
   |0000..............................0000|FFFF|    IPv4 address     |
   +--------------------------------------+----+---------------------+

   See [RFC4038] for background on the usage of the "IPv4-mapped IPv6
   address".
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