Despite its graceful bandwidth saving nature, IP multicast has not been successful in widely spreading and using. Challenging includes policy and technological issues such as inter-domain routing, multicast availability and reachability. Properly detecting and isolating the faults would be the first step to stabilize IP multicast. In this paper, we introduce a scalable multicast monitoring framework. To efficiently cope with multicast network and networking problems, it enlarges its monitoring scopes from collecting delivery statistics to verifying end-to-end multicast availability, reachability and interactivity. We carry out various networking experiments to verify the scalability and feasibility of the proposed framework.