H3C Technologies H3C S10500 Series Switches - Manual (Page 29)

14
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 device that runs IGMP snooping establishes mappings
between ports and multicast MAC addresses, and forwards multicast data based on these mappings.
As shown in
Figure 11 , when IGMP snooping is not running on the switch, multicast packets are flooded
to all devices at Layer 2. When IGMP snooping runs on the switch, multicast packets for known multicast
groups are multicast to the receivers, rather than being broadcast to all hosts, at Layer 2.
Figure 11 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 requiring the data at Layer 2. It has the
following advantages:
• Reducing Layer 2 broadcast packets, thus saving network bandwidth
• Enhancing the security of multicast traffic
• Facilitating the implementation of per-host accounting