H3C Technologies H3C S10500 Series Switches - Manual (Page 25)

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Figure 8 Positions of Layer 3 multicast protocols
1. Multicast group management protocols
Typically, the Internet Group Management Protocol (IGMP) or Multicast Listener Discovery Protocol (MLD)
is used between hosts and Layer 3 multicast devices that directly connect to the hosts. These protocols
define the mechanism of establishing and maintaining group memberships between hosts and Layer 3
multicast devices.
2. Multicast routing protocols
A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast routes
and forward multicast packets correctly and efficiently. Multicast routes constitute loop-free data
transmission paths from a data source to multiple receivers, namely, a multicast distribution tree.
In the ASM model, multicast routes include intra-domain routes and inter-domain routes.
• An intra-domain multicast routing protocol discovers multicast sources and builds multicast
distribution trees within an AS to deliver multicast data to receivers. Among a variety of mature
intra-domain multicast routing protocols, Protocol Independent Multicast (PIM) is most widely used.
Based on the forwarding mechanism, PIM has dense mode—often referred to as “PIM-DM”—and
sparse mode—often referred to as “PIM-SM”.
• An inter-domain multicast routing protocol is used for delivery of multicast information between two
ASs. So far, mature solutions include Multicast Source Discovery Protocol (MSDP) and Multicast
Border Gateway Protocol (MBGP). MSDP propagates multicast source information among different
ASs. MBGP is an extension of the Multiprotocol Border Gateway Protocol (MP-BGP) for exchanging
multicast routing information among different ASs.
For the SSM model, multicast routes are not divided into intra-domain routes and inter-domain routes.
Because receivers know the position of the multicast source, channels established through PIM-SM are
sufficient for the transport of multicast information.
Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM snooping,
multicast VLAN, and IPv6 multicast VLAN.