Abstract: In distributed network applications such as multiparty teleconferencing, users often need to send the same message to several other users. To achieve such one-to-many or many-to-many communication efficiently in wide-area internetworks, it is imperative to support multicasting, i.e., concurrent sending of messages from one source to multiple receivers. The current IP architecture for multicast routing, the core-based tree (CBT) protocol, and protocol independent multicast (PIM) protocol save a number of limitations for very large internets. To eliminate their limitations, we propose a new multicast routing protocol, called scalable Internet multicast protocol (SIMP).