RGMP is designed to work in conjunction with multicast routing protocols that support distribution tree Join/Prune. Its typical companion protocol is PIM-SM.
The RGMP protocol specifies only IPv4 multicast routing operations and does not cover IPv6. Cisco’s Router-Port Group Management Protocol addresses the shortcomings of the Internet Group Management Protocol in its snooping mechanism.
I. RGMP operates between multicast routers and switches. Through RGMP, multicast data packets forwarded in the switch can be constrained to only the routers that need them. RGMP is designed for backbone switching environments with multiple interconnected routers. The primary technical limitation is that this technique can only constrain multicast traffic to switch ports that are directly or indirectly connected to receivers via other switches. Under IGMP snooping, multicast traffic cannot be constrained at ports connected to at least one multicast router, thus causing multicast traffic flooding on those ports.
II. This is an inherent limitation of the IGMP snooping mechanism. Because of this, routers cannot report traffic status, so switches only know the types of multicast traffic requested by hosts, but not the types of traffic received on router ports. The RGMP protocol supports constraining multicast traffic to router ports. To efficiently achieve traffic constraint, both network switches and routers must support RGMP.
Through RGMP, the backbone switch can learn the multicast group types required on each port, and the multicast router then transmits this information to the switch. However, routers only send RGMP messages and ignore the RGMP messages they receive.
III. When a group no longer needs to receive traffic, the router sends an RGMP leave message. In the RGMP protocol, network switches must consume a network port to intercept RGMP messages and process them. Furthermore, switches in RGMP are not allowed to forward/flood received RGMP messages to other network ports. RGMP is designed to work in conjunction with multicast routing protocols that support distribution tree Join/Prune.
If you need to know information about specific routing entries, you can append the addresses of those specific routing entries to the request message and send it