TCP/IP is currently the standard network protocol for wired Internet. To make all Internet services available to all mobile users, a Mobile IP is proposed. Another important development for TCP/IP is the evolution to the next generation Internet, the protocol for which is called IPv6. Whether using IPv4 or IPv6, situations arise in some Internet applications where a piece of data needs to be sent to multiple recipients, a process called multicasting. In this paper, we study the multicasting routing problem based on Mobile IPv6. In multicasting, the mobility of a sender may lead to serious problems. When the sender moves, the full delivery tree may fail so that multicast datagrams cannot be forwarded to all receivers. In this paper, we propose a Reverse Traffic Interface (RTI) mechanism to preserve the integrity of the multicast tree. In this mechanism, we will use a Backward-Forced Path (BFP) to regenerate a new tree without rerouting. It can ensure multicast datagrams are sent to all reachable destinations without interruption. In addition, we show that a slight modification of the DVMRP (Distance Vector Multicast Routing Protocol), called DVMRPv6, can be used in Mobile IPv6 to support our mechanism. Finally, we use a total tree cost measure to estimate and evaluate our scheme. We also implement simulations to demonstrate its effectiveness. The results show that our proposal makes multicasting on mobiles network simpler, more efficient, and more reliable.