One of major reasons why IP multicast has not been well deployed is the complexity of IP multicast routing. Since existing IP multicast routing protocols have been designed independently of IP unicast routing protocols, a router must maintain routing tables for both IP multicast and unicast routing. This is, in particular, a big burden for an inter-domain router. In addition, by using existing IP multicast routing protocols, we cannot realize an application that a sending host outside the designated domain sends IP multicast packets only towards the designated domain.

To resolve above issues, we propose a new architecture for IP multicast, which is called Domain Constrained Multicast (DCM). In this architecture, IP multicast packets are forwarded to a border router of the designated domain, using the existing routing mechanisms of IP unicast such as BGP-4. And then IP multicast packets are delivered inside the designated domain using the existing routing mechanisms of IP multicast such as PIM-SM. Since IPv4 address is limited regarding flexibility and extensibility, we describe the realization of the DCM architecture over IPv6. We describe the extension of the DCM architecture for applying it to inter-domain routing. We have compared the DCM architecture with existing inter-domain IP multicast routing protocols such as MSDP and BGMP. Since the DCM architecture utilizes the existing BGP-4 infrastructure for the inter-domain routing, its deployment is fairly easy, when compared with them. The DCM architecture is the first attempt that fully integrates the advantages of IP multicast and unicast.