Abstract: Forwarding state proportional to the number of multicast groups may cause the scalability problem of multicast routing protocols. Existing intra-group forwarding state reduction approaches for sparse mode multicast, which aim to remove forwarding states at non-branching routers, are analyzed, and some problems appearing in these schemes are presented. A new forwarding state reduction scheme is proposed, which reduces storage requirement of multicast forwarding state by dynamically modifying the format of each interface in the multicast forwarding table entries according to the location and number of branching points on the multicast tree.