Igmp Snooping Overview - Huawei Quidway s3700 series Configuration Manual

Quidway S3700 Series Ethernet Switches
Configuration Guide - Multicast

2.1 IGMP Snooping Overview

This section describes the functions and advantages of the IGMP snooping protocol.
IGMP Snooping Function
Internet Group Management Protocol Snooping (IGMP snooping) is a Layer 2 multicast
protocol. The IGMP snooping protocol maintains information about the outgoing interfaces of
multicast packets by listening to multicast protocol packets exchanged between the router and
hosts. Thus the IGMP snooping protocol manages and controls the forwarding of multicast
packets.
After receiving multicast packets from an upstream device, an Ethernet device at the edge of the
access network forwards the multicast packets to multicast receivers. As shown in
multicast data is broadcast at the data link layer by default, which wastes network bandwidth
and causes multicast data to be sent to unpaid subscribers.
If IGMP snooping is configured on the Layer 2 device, multicast data of a known group is
forwarded to specified receivers (paid subscribers) but not broadcast at the data link layer.
Figure 2-1 Comparison before and after IGMP snooping is configured on a Layer 2 device
Source
Issue 01 (2011-10-26)
Multicast packet transmission
without IGMP Snooping
Router
PIM
Reciever A
Multicast Packet
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Copyright © Huawei Technologies Co., Ltd.
Multicast packet transmission
when IGMP Snooping runs
Source
PIM
Switch
Reciever B
Reciever A
2 IGMP Snooping Configuration
Figure
Router
Switch
Reciever B
2-1,
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