H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 10)

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Configuring 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.
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.
Without IGMP snooping running on the access controller (AC), multicast packets are flooded to wireless
clients. When IGMP snooping runs on the AC, multicast packets for known multicast groups are multicast
to the wireless clients that need the traffic, rather than being flooded to all wireless clients attached to it.
This feature improves bandwidth efficiency, enhances multicast security, and helps per-host accounting
for multicast users.
As shown in
Figure 1 , an access point (AP) joins three different extended service sets (ESSs),
corresponding to wireless clients Client A, Client B, and Client C. Without IGMP snooping enabled on
the AC, Client A, Client B, and Client C can receive multicast data. With IGMP snooping enabled on the
AC, only Client A and Client C can receive multicast data.
For information about WLAN-DBSS interfaces, see WLAN Configuration Guide.
Figure 1 Before and after IGMP snooping is enabled on the AC