Chapter 2 Igmp Snooping Configuration; Igmp Snooping Overview; Principle Of Igmp Snooping - H3C S3100 8C SI Operation Manual

Operation Manual – Multicast
H3C S3100 Series Ethernet Switches

Chapter 2 IGMP Snooping Configuration

2.1 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.

2.1.1 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
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.
Multicast packet transmission
Source
Host A
Receiver
Figure 2-1 Before and after IGMP Snooping is enabled on Layer 2 device
Figure 2-1, when IGMP Snooping is not running on the switch, multicast
without IGMP Snooping
Multicast router
Layer 2 switch
Host C
Receiver
Host B
Multicast packets
Chapter 2 IGMP Snooping Configuration
Multicast packet transmission
when IGMP Snooping runs
Source
Host A
Receiver
2-1
Multicast router
Layer 2 switch
Host C
Receiver
Host B