Cisco Group Management Protocol

Cisco Group Management Protocol (CGMP) is another widely used protocol to forward multicast traffic to appropriate ports. CGMP is a Cisco proprietary protocol. The router communicates IGMP information with the switch via the CGMP protocol at Layer 2. Unlike IGMP snooping, CGMP-enabled switches do not have any insight into the Layer 3 IGMP packet types. All IGMP information is forwarded to the router, which in turn sends a Layer 2 message informing the switch regarding client participation for multicast traffic. The router translates the IGMP report into a CGMP message and forwards it to the switch. Based on what is contained in the CGMP packet, the switch will either add or delete port(s) for the multicast stream. ...

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