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Configuring IGMP snooping
Overview
Internet Group Management Protocol (IGMP) snooping is a multicast constraining mechanism that runs
on Layer 2 devices to manage and control multicast groups.
By analyzing received IGMP messages, a Layer 2 device that runs IGMP snooping establishes mappings
between ports and multicast MAC addresses, and forwards multicast data based on these mappings.
As shown in Figure 11, w
ithout IGMP snooping enabled, the Layer 2 switch floods multicast packets to all
devices at Layer 2. With IGMP snooping enabled, the Layer 2 switch forwards multicast packets for
known multicast groups to only the receivers that require the multicast data at Layer 2. This feature
improves bandwidth efficiency, enhances multicast security, and helps per-host accounting for multicast
users.
Figure 11 Before and after IGMP snooping is enabled on the Layer 2 device
Basic concepts in IGMP snooping
IGMP snooping related ports
As shown in Figure 12, Router A connects to the multicast source, IGMP snooping runs on Switch A and
Switch B, and Host A and Host C are receiver hosts as members of a multicast group.
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