7
The following describes the fields of an IPv6 multicast address:
0xFF
—The most significant eight bits are 11111111.
Flags
—The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit
Description
0
Reserved, set to 0.
R
•
When set to 0, this address is an IPv6 multicast address
without an embedded RP address.
•
When set to 1, this address is an IPv6 multicast address with
an embedded RP address. (The P and T bits must also be set
to 1.)
P
•
When set to 0, this address is an IPv6 multicast address not
based on a unicast prefix.
•
When set to 1, this address is an IPv6 multicast address
based on a unicast prefix. (The T bit must also be set to 1.)
T
•
When set to 0, this address is an IPv6 multicast address
permanently-assigned by IANA.
•
When set to 1, this address is a transient or dynamically
assigned IPv6 multicast address.
Scope
—The Scope field contains four bits, which represent the scope of the IPv6
internetwork for which the multicast traffic is intended.
Table 5 Values of the Scope field
Value
Meaning
0, F
Reserved.
1
Interface-local scope.
2
Link-local scope.
3
Subnet-local scope.
4
Admin-local scope.
5
Site-local scope.
6, 7, 9 through D
Unassigned.
8
Organization-local scope.
E
Global scope.
Group ID
—The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast
group in the scope that the Scope field defines.
Ethernet multicast MAC addresses
•
IPv4 multicast MAC addresses:
As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are
0x01005E. Bit 25 is 0, and the other 23 bits are the least significant 23 bits of an IPv4 multicast
address.
0 R P T
