This protocol is a stateful
280 Chapter 7: Managing Address Spaces with NAT and IPv6
counterpart to IPv6 stateless address autocon?¬?guration (RFC 2462), and it can be used
separately or concurrently with IPv6 stateless address autocon?¬?guration to obtain
con?¬?guration parameters.
Use of EUI-64 Format in IPv6 Addresses
The 64-bit interface identi?¬?er in an IPv6 address identi?¬?es a unique interface on a link. A
link is a network medium over which network nodes communicate using the link layer. The
interface identi?¬?er can also be unique over a broader scope. In many cases, an interface
identi?¬?er is the same as, or is based on, the link-layer (MAC) address of an interface. As in
IPv4, a subnet pre?¬?x in IPv6 is associated with one link. Figure 7-11 illustrates the IPv6
EUI-64 interface identi?¬?er.
Figure 7-11 IPv6 EUI-64 Interface Identi?¬?er
Interface identi?¬?ers in global unicast and other IPv6 address types must be 64 bits long
and can be constructed in the 64-bit EUI-64 format. The EUI-64 format interface ID is
derived from the 48-bit link-layer (MAC) address by inserting the hexadecimal number
FFFE between the upper 3 bytes (Organizational Unique Identi?¬?er [OUI] ?¬?eld) and the
lower 3 bytes (serial number) of the link layer address.
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