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IPv6 Overview 659
node may fill this address in the source address field of an IPv6 packet, but may
not use it as a destination IPv6 address.
Multicast address
IPv6 multicast addresses listed in Table 37 are reserved for special purpose.
Besides, there is another type of multicast address: solicited-node address. A
solicited-node multicast address is used to acquire the link-layer addresses of
neighbor nodes on the same link, and is also used for duplicate address detection
(DAD). Each IPv6 unicast or anycast address has one corresponding solicited-node
address. The format of a solicited-node multicast address is:
FF02:0:0:0:0:1:FFXX:XXXX. Where, FF02:0:0:0:0:1 FF is permanent and consists of
104 bits, and XX:XXXX is the last 24 bits of an IPv6 unicast or anycast address.
Interface identifier in IEEE EUI-64 format
Interface identifiers in IPv6 unicast addresses are used to identify interfaces on a
link and they are required to be unique on that link. Interface identifiers in IPv6
unicast addresses are currently required to be 64 bits long. An interface identifier
in IEEE EUI-64 format is derived from the link-layer address of that interface.
Interface identifiers in IPv6 addresses are 64 bits long, while MAC addresses are 48
bits long. Therefore, the hexadecimal number FFFE needs to be inserted in the
middle of MAC addresses (behind the 24 high-order bits). To ensure the interface
identifier obtained from a MAC address is unique, it is necessary to set the
universal/local (U/L) bit (the seventh high-order bit) to “1”. Thus, an interface
identifier in IEEE EUI-64 format is obtained.
Figure 195 Convert a MAC address into an EUI-64 interface identifier
Introduction to IPv6
Neighbor Discovery
Protocol
IPv6 neighbor discovery protocol (NDP) uses five types of ICMPv6 messages to
implement the following functions:
■
“Address resolution” on page 660
Table 37 Reserved IPv6 multicast addresses
Address Application
FF01::1 Node-local scope all-nodes multicast address
FF02::1 Link-local scope all-nodes multicast address
FF01::2 Node-local scope all-routers multicast address
FF02::2 Link-local scope all-routers multicast address
FF05::2 Site-local scope all-routers multicast address
MAC address:
0012-3400-ABCD
Represented in binary :
0000000000010010 0011010000000000 1010101111001101
Insert FFFE:
0000000000010010 0011010011111111 1111111000000000 1010101111001101
Set U /L bit:
0000001000010010 0011010011111111 1111111000000000 1010101111001101
EUI-64 address:
0212:34FF:FE00:ABCD