3Com S7906E - Switch, Configuration Manual

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Table 1-4 Description on the bits of the Flags field
Bit Description
0 Reserved, set to 0
R
z
When set to 0, it indicates that this address is an IPv6 multicast address without
an embedded RP address
z
When set to 1, it indicates that this address is an IPv6 multicast address with an
embedded RP address (The P and T bits must also be set to 1)
P
z
When set to 0, it indicates that this address is an IPv6 multicast address not
based on a unicast prefix
z
When set to 1, it indicates that this address is an IPv6 multicast address based
on a unicast prefix (the T bit must also be set to 1)
T
z
When set to 0, it indicates that this address is an IPv6 multicast address
permanently-assigned by IANA
z
When set to 1, it indicates that this address is a transient, or dynamically
assigned IPv6 multicast address
z
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 .
Table 1-5 Values of the Scope field
Value Meaning
0, 3, F Reserved
1 Interface-local scope
2 Link-local scope
4 Admin-local scope
5 Site-local scope
6, 7, 9 through D Unassigned
8 Organization-local scope
E Global scope
z
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 .