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Configuring IGMP snooping
This chapter describes IGMP snooping, how to configure IGMP snooping, configuration examples,
troubleshooting methods, and an appendix about processing multicast protocol messages.
Overview
IGMP snooping is a multicast constraining mechanism that runs on Layer 2 devices to manage and
control multicast groups.
By analyzing received IGMP messages, an IGMP snooping-enabled Layer 2 device establishes
mappings between ports and multicast MAC addresses, and forwards multicast data based on these
mappings.
As shown in
, without 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 destined for known multicast groups are multicast 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
IGMP snooping basic concepts
This section describes the basic concepts involved in IGMP snooping.
IGMP snooping related ports
As shown in
, 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.