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IGMP SNOOPING CONFIGURATION
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.
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 Figure 62, when IGMP Snooping is not running on the switch,
multicast 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.
Figure 62 Before and after IGMP Snooping is enabled on Layer 2 device
Basic Concepts in IGMP
Snooping
IGMP Snooping related ports
As shown in Figure 63, Router A connects to the multicast source, IGMP Snooping
runs on Switch A and Switch B, Host A and Host C are receiver hosts (namely,
multicast group members).
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