H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – Multicast
H3C S7500E Series Ethernet Switches Chapter 1 Multicast Overview
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assigned by IANA; when set to 1, the T flag indicates a transient, or dynamically
assigned 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 1-4.
z Reserved: 80 bits, all set to 0 currently.
z Group ID: 112 bits, identifying the multicast group. For details about this field, refer
to RFC 3306.
Table 1-4 Values of the Scope field
Value Meaning
0, 3, F Reserved
1 Node-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
III. 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 0x0, 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 1-5.