| 8 | 4 | 4 | 112 bits |
+----------+----+----+-----------------------------------------------------------------+
|11111111|flgs|scop| group ID |
+----------+----+----+-----------------------------------------------------------------+
The first byte of the address format is full 1, which denote a multicast address.
Flag field:
It consists of 4 bits. At present, only the fourth bit is specified. The bit is used to indicate
whether the address is a known multicast address specified by Internet Number Constitution
or a temporary multicast address used in a specific condition. If this flag bit is 0, it indicates
this address is a known multicast address. If this bit is 1, it indicates that this address is a
temporary one. Other 3 flag bits are reserved for future use.
Range field:
Composed of 4 bits and used to denote the range of multicast. Namely, whether the
multicast group contains the local node, the local link and the local site or any position nodes
in the IPv6 global address space.
Group Identifier field:
112 bits long and used to identify a multicast group. Depending on whether a multicast
address is temporary or known and the range of the address, a multicast identifier can
denote different groups.
The multicast address of the IPv6 is this type of address taking FF00::/8 as the prefix One
multicast address of an IPv6 usually identifies the interfaces of a serial of different nodes.
When one message is sent to one multicast address, this message will be distributed to the
interfaces of each node with this multicast address. One node (host or router) should add the
following multicast:
The multicast address of all nodes for the local link is FF02::1
The prefix of the multicast address for the solicited node is
FF02:0:0:0:0:1:FF00:0000/104
If they are routers, it is necessary to add the multicast address FF02::2 of all routers for the
local link.
The multicast address of the solicited node corresponds to the IPv6 unicast and anycast
address, so it is necessary for the IPv6 node to add corresponding multicast address of the
solicited node for each configured unicast address and anycast address. The prefix of the
multicast address for the solicited node is FF02:0:0:0:0:1:FF00:0000/104, another 24 bits
are comprised of the unicast address or the lower 24 bits of the anycast address, for
instance, the multicast address of the solicited node corresponding to the
FE80::2AA:FF:FE21:1234 is FF02::1:FF21:1234,
The multicast address of solicited node is usually used to the neighbor solicitation (NS)
message. The format of the solicited node is shown as follows:
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