To tackle the high requirement to network infrastructure, lack of scalability, address conflict and security vulnerability problems of IP multicast protocols, this paper introduces CMSM, a novel closed multi-source IP Multicast protocol. It is a lightweight self-configurable multi-source multicast paradigm for the Internet. After being aware of a specific source for a many-to-many group, the hosts and the routers send their JOIN/REQS/LEAVE message towards the source, and a closed hybrid multi-source-multi-receiver CMSM tree used for secure group communication is formed in an open network infrastructure. Non-CMSM routers are bypassed by CMSM tunnels, which eliminates the dependence of multicast-specific routing. Only authorized senders or receivers are allowed to send to or receive from CMSM group and only trusted routers are allowed to be the branch points of CMSM tree. Analyses show that CMSM is high scalability and reachability, and has preferable security features.