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Bit Description

• When set to 0, it indicates that this address is an IPv6 multicast address

permanently-assigned by IANA.

• When set to 1, it indicates that this address is a transient, or dynamically assigned IPv6

multicast address.

• Scope—The Scope field contains four bits, which indicate that 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

When a unicast IP packet is transmitted over Ethernet, the destination MAC address is the MAC address

of the receiver. When a multicast packet is transmitted over Ethernet, the destination address is a

multicast MAC address because the packet is directed to a group formed by a number of receivers,

rather than to one specific receiver.

1. 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 least-significant 23 bits are the least-significant 23 bits of a multicast IPv4 address.

Figure 6 IPv4-to-MAC address mapping

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 110 111

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