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IGMP snooping configuration

This chapter includes these sections:

• IGMP snooping overview

• IGMP snooping configuration task list

• Displaying and maintaining IGMP snooping

• IGMP snooping configuration examples

• Troubleshooting IGMP snooping configuration

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.

Principle of IGMP snooping

By analyzing received IGMP messages, a Layer 2 switch that is running IGMP snooping establishes

mappings between ports and multicast MAC addresses, and forwards multicast data based on these

mappings.

When IGMP snooping is not running on the switch, multicast packets are flooded 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.

Figure 10 Before and after IGMP snooping is enabled on the Layer 2 device

Multicast packet transmission

without IGMP Snooping

Source

Multicast router

Host A

Receiver

Host B

Host C

Receiver

Multicast packets

Layer 2 switch

Multicast packet transmission

when IGMP Snooping runs

Source

Multicast router

Host A

Receiver

Host B

Host C

Receiver

Layer 2 switch

IGMP snooping forwards multicast data to only the receivers that require the data at Layer 2. It brings the

following advantages:

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H3c-technologies H3C S3100V2 Series Switches Manuel d'utilisateur Page 20