Operation Manual – Multicast
H3C S3100 Series Ethernet Switches Chapter 1 Multicast Overview
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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 a loop-free data transmission path from a data source to multiple receivers,
namely a multicast distribution tree.
In the ASM model, multicast routes come in intra-domain routes and inter-domain
routes.
z An intra-domain multicast routing protocol is used to discover multicast sources
and build multicast distribution trees within an autonomous system (AS) so as to
deliver multicast data to receivers. Among a variety of mature intra-domain
multicast routing protocols, protocol independent multicast (PIM) is a popular one.
Based on the forwarding mechanism, PIM comes in two modes – dense mode
(often referred to as PIM-DM) and sparse mode (often referred to as PIM-SM).
z 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).
For the SSM model, multicast routes are not divided into inter-domain routes and
intra-domain routes. Since receivers know the position of the multicast source,
channels established through PIM-SM are sufficient for multicast information transport.
II. Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP Snooping and multicast VLAN. Figure 1-6
shows where these protocols are in the network.
Source
Receiver Receiver
multicast packets
IGMP Snooping
Figure 1-6 Positions of Layer 2 multicast protocols
Running on Layer 2 devices, Internet Group Management Protocol Snooping (IGMP
Snooping) are multicast constraining mechanisms that manage and control multicast
groups by listening to and analyzing IGMP messages exchanged between the hosts
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