H3C Technologies H3C S3600 Series Switches - Manual (Page 450)

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6
IGMP Snooping Configuration
When configuring IGMP snooping, go to these sections for information you are interested in:
z IGMP Snooping Overview
z Configuring IGMP Snooping
z Displaying and Maintaining IGMP Snooping
z IGMP Snooping Configuration Examples
z Troubleshooting IGMP Snooping
In this manual, the term “router” refers to a router in the generic sense or a Layer 3 Ethernet switch
running an IP multicast protocol.
IGMP Snooping Overview
Internet Group Management Protocol Snooping (IGMP Snooping) is a multicast constraining
mechanism that runs on Layer 2 devices to manage and control multicast groups.
Principle of IGMP Snooping
By analyzing received IGMP messages, a Layer 2 device running IGMP Snooping establishes
mappings between ports and multicast MAC addresses and forwards multicast data based on these
mappings.
As shown in Figure 6-1 , when IGMP Snooping is not running on the switch, multicast packets are
broadcast to all devices at Layer 2. When IGMP Snooping is running on the switch, multicast packets for
known multicast groups are multicast to the receivers, rather than broadcast to all hosts, at Layer 2.
However, multicast packets for unknown multicast groups are still broadcast at Layer 2.