H3C Technologies H3C S3100V2 Series Switches - Manual (Page 20)

12
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: