H3C Technologies H3C S3100 Series Switches - Manual (Page 236)

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch Chapter 1 Multicast Overview
1-9
The high-order four bits of the IP multicast address are 1110, representing the multicast
ID. Only 23 bits of the remaining 28 bits are mapped to a MAC address. Thus, five bits
of the multicast IP address are lost. As a result, 32 IP multicast addresses are mapped
to the same MAC address.
1.2.2 IP Multicast Protocols
IP multicast protocols include the multicast group management protocol and the
multicast routing protocol. Figure 1-6 describes the positions of the protocols related to
multicast in the network.
Server
Multicast User D
r E Use
User C
IGMP
IGMP
User A
User B
IGMP
MBGP/MSDP
PIM
PIM
AS1
AS2
Server
Multicast User D
r E Use
User C
IGMP
IGMP
User A
User B
IGMP
Server
Multicast User D
r E Use
User C
IGMP
IGMP
User A
User B
IGMP
MBGP/MSDP
PIM
PIM
AS1
AS2
Figure 1-6
Positions of protocols related to multicast
I. Multicast group management protocol
Internet group membership protocol (IGMP) is adopted between hosts and multicast
routers. This protocol defines the mechanism of establishing and maintaining group
membership between hosts and multicast routers.
II. Multicast routing protocols
A multicast routing protocol operates between multicast routers to establish and
maintain multicast routes and forward multicast packets accurately and effectively. A
multicast route establishes a loop-free data transport path from a data source to
multiple receivers. The task of multicast routing protocol is to establish a distribution
tree structure. Multicast routers can establish the data transmission path (namely,
distribution tree) in many ways.
Like unicast routes, multicast routes come in intra-domain routes and inter-domain
routes. Intra-domain multicast routes are quite mature now. Protocol independent
multicast (PIM) is the most commonly used protocol currently. It can cooperate with any
unicast routing protocol.