Cisco Group Management Protocol (CGMP) is a Cisco proprietary Layer 2 protocol used for Layer 2 efficiency at layer 2.
Basically whenever a host want to join a multicast group, it send IGMP Join message to the target group. This message goes to the multicast router.
After such records, whenever a multicast activity is done, these CAM table is used.
In the working mechanims of CGMP, switches only listens the CGMP messages coming from the router. With these messages, they manage the efficient group membership facilities.
CGMP need to be configured on both Layer 2 switches and Layer 3 Routers.
Now, let’s show this configuration with an example.