Endereços IPv6 UNICAST
----------------------

De acordo com o RFC 3687 (Agosto de 2003), todos os 
endereços 2000::/3 são válidos para unicast.

An example of the resulting format of global unicast address under
the 2000::/3 prefix that is currently being delegated by the IANA 
and consistent with the recommendations in RFC 3177 is:

 | 3 |     45 bits         |  16 bits  |       64 bits              |
 +---+---------------------+-----------+----------------------------+
 |001|global routing prefix| subnet ID |       interface ID         |
 +---+---------------------+-----------+----------------------------+

where:
- the routing prefix is a value assigned to identify a site 
  (a cluster of subnets/links);
- the subnet ID is an identifier of a subnet within the site; 
- the interface ID is a modified EUI-64 format as defined in [ARCH].


Transformação de um endereço IEEE MAC de 48 bit em formato EUI-64
-----------------------------------------------------------------

Pode ser usado para formar o endereço interface ID da figura
de cima. O formato EUI-64 encontra-se definido em,
 - IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
   Registration Authority",
   http://standards.ieee.org/regauth/oui/tutorials/EUI64.html,
   March 1997.

The EUI-64 defines a method to create a IEEE EUI-64 identifier from an
IEEE 48bit MAC identifier.  This is to insert two octets, with
hexadecimal values of 0xFF and 0xFE, in the middle of the 48 bit MAC
(between the company_id and vendor supplied id).  For example, the 48
bit IEEE MAC with global scope:

 |0              1|1              3|3              4|
 |0              5|6              1|2              7|
 +----------------+----------------+----------------+
 |cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|
 +----------------+----------------+----------------+

where "c" are the bits of the assigned company_id, "0" is the value
of the universal/local bit to indicate global scope, "g" is
individual/group bit, and "m" are the bits of the manufacturer-
selected extension identifier.  The interface identifier would be of
the form:

   |0              1|1              3|3              4|4              6|
   |0              5|6              1|2              7|8              3|
   +----------------+----------------+----------------+----------------+
   |cccccc1gcccccccc|cccccccc11111111|11111110mmmmmmmm|mmmmmmmmmmmmmmmm|
   +----------------+----------------+----------------+----------------+

When IEEE 802 48bit MAC addresses are available (on an interface or a
node), an implementation may use them to create interface identifiers
due to their availability and uniqueness properties.