Multicast Cisco Group Management Protocol
Cisco Group Management Protocol or CGMP is a Cisco proprietary protocol used on Cisco routers and multilayer switches that are connected to Layer 2 switches to perform tasks similar to those performed by IGMP.
CGMP permits Layer 2 group membership information to be communicated from the CGMP server to the switch. The switch can then learn on which interfaces multicast members reside instead of flooding multicast traffic to all switch interfaces. (IGMP snooping is another method to constrain the flooding of multicast packets.)
CGMP is generally used whenever IGMP snooping is not supported by a switching device.