3Com 4510G Configuration Manual page 390

Bit
When set to 0, it indicates that this address is an IPv6 multicast address
permanently-assigned by IANA
T
When set to 1, it indicates that this address is a transient, or dynamically
assigned IPv6 multicast address
Scope: 4 bits, indicating the scope of the IPv6 internetwork for which the multicast traffic is
intended. Possible values of this field are given in
Table 1-5 Values of the Scope field
0, 3, F
1
2
4
5
6, 7, 9 through D
8
E
Group ID: 112 bits, IPv6 multicast group identifier that uniquely identifies an IPv6 multicast group
in the scope defined by the Scope field.
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, however, 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 high-order 24 bits of an IPv4 multicast MAC address are 0x01005E, bit 25 is 0,
and the low-order 23 bits are the low-order 23 bits of a multicast IPv4 address. The IPv4-to-MAC
mapping relation is shown in
Figure 1-6 IPv4-to-MAC address mapping
32-bit IPv4 address
48-bit MAC address
0000 0001 0000 0000
25-bit MAC address prefix
Value
Figure 1-6.
5 bits lost
XXXX X
1110 XXXX XXXX XXXX
0101 1110 0XXX XXXX
Description
Table 1-5.
Reserved
Interface-local scope
Link-local scope
Admin-local scope
Site-local scope
Unassigned
Organization-local scope
Global scope
XXXX XXXX
23 bits
...
mapped
XXXX XXXX
2-9
Meaning
XXXX XXXX
...
XXXX XXXX