MSDP is the correct feature when multicast receivers in one autonomous system must be able to learn and receive content from sources in another autonomous system. The scenario describes separate multicast frameworks close to the receivers in each AS and requires source resiliency across AS boundaries. In PIM Sparse Mode, a local RP learns about sources registered in its own domain. MSDP allows RPs in different domains to exchange Source-Active information, enabling receivers in one domain to discover and join toward sources that exist in another domain. Anycast RP is primarily a redundancy and load-sharing technique for RPs, often inside a multicast domain, but it does not by itself provide interdomain source discovery for independent ASs. SSM can be efficient when receivers know the source, but the question emphasizes RP-based framework placement and source availability between ASs. BIDIR-PIM is for scalable many-to-many shared-tree forwarding, not interdomain source discovery. Therefore, the design should include MSDP. Reference topics: MSDP, interdomain multicast, PIM-SM, Source-Active exchange, RP resilience across autonomous systems.