Scalability of multicast forwarding state is likely to be a major issue facing inter-domain multicast deployment. We present a comprehensive analysis of the multicast forwarding state problem. Our goal is to understand the scaling trends of multicast forwarding state in the Internet, and to explore the intuitions that have motivated state reduction research. We conducted simulation experiments on both real and generated network topologies, with a range of parameters driven by multicast application characteristics. We found that the increase in peering among Internet backbone networks has led to more multicast forwarding state at a handful of core domains, but less state in the rest of the domains. We observed that scalability of multicast forwarding state with respect to session size follows a power law. Our findings show that distribution and concentration of multicast forwarding state in the Internet is significantly, impacted by the application characteristics. We investigated the proposals on non-branching multicast forwarding state elimination, and found substantial reduction is attainable even with very dense multicast sessions.