To ensure that the chosen address is
from a unique Ethernet MAC address, the seventh bit in the high-order byte is set to 1 to
indicate the uniqueness of the 48-bit address.
Stateless autocon?¬?guration is a key feature of IPv6. It enables serverless basic con?¬?guration
of the nodes and easy renumbering.
Stateless autocon?¬?guration uses the information in the router advertisement messages to
con?¬?gure the node. The pre?¬?x included in the router advertisement is used as the /64 pre?¬?x
for the node address. The other 64 bits are obtained by the dynamically created interface
identi?¬?er, which in the case of Ethernet, is the modi?¬?ed EUI-64 format.
Routers periodically send router advertisements. When a node boots up, the node needs its
address in the early stage of the boot process. It can be ???long??? to wait for the next router
advertisement to get the information to con?¬?gure its interfaces. Instead, a node sends a
router solicitation message to the routers on the network asking them to reply immediately
with a router advertisement so the node can immediately autocon?¬?gure its IPv6 address. All
U/L Bit Where U =
1 = Universally Unique
0 = Locally Unique
U = 1
02 90 27 FF FE 17 FC 0F Modified EUI-64 Address
000000UG
Transitioning to IPv6 281
the routers respond with a normal router advertisement message with the all-nodes
multicast address as the destination address.
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