Huawei Quidway S6500 Series Operation Manual page 290

Operation Manual - Multicast Protocol
Quidway S6500 Series Ethernet Switches
II. Ethernet Multicast MAC Addresses
When a unicast IP packet is transmitted on the Ethernet, the destination MAC address
is the MAC address of the receiver. However, for a multicast packet, the destination is
no longer a specific receiver but a group with unspecific members. Therefore, the
multicast MAC address should be used.
As Internet Assigned Number Authority (IANA) provisions, the high 24 bits of a
multicast MAC address are 0x01005e and the low 23 bits of a MAC address are the low
23 bits of a multicast IP address.
32 bits IP address
48 bits MAC address
XXXX
X X X X
Figure 1-4 Mapping between a multicast IP address and an Ethernet MAC address
The first four bits of the multicast address are 1110, representing the multicast identifier.
Among the rest 28 bits, only 23 bits are mapped to the MAC address, and the other five
bits are lost. This may results in that 32 IP addresses are mapped to the same MAC
address.
1.2.2 IP Multicast Protocols
Multicast involves multicast group management protocols and multicast routing
protocols. Their application positions are shown in Figure 1-5 Application positions of
multicast-related protocols.
Server
Figure 1-5 Application positions of multicast-related protocols
111 0
XX XX
5 bits not mapped
XXXX XXXX
X X X X XXX X
Multicast
AS2
Huawei Technologies Proprietary
XXXX XXXX
XXX X XX XX
Lower 23 bits directly mapped
XXXX XXXX
XXXX XX XX
AS1
IGMP
PIM
MBGP/MSDP
IGMP
PIM
IGMP
User E
1-6
Chapter 1 Multicast Overview
XXXX
X X X X
XXXX
X X X X
User A
User B
User C
User D