Internet multicasting is the delivery of an internet packet to all members of a group within the internet. A multicast group includes members in more than one network and host. This thesis identifies requirements for internet multicasting, proposes the mechanism solving the problem of multicasting in the internet environment, and analyzes the performance. The internet multicast mechanism is considered in the internet sublayer, which is the layer of commonality that unifies all of the different networks that might be used in the lower layer. In order to support the multidestination addressing capability, the internet packet header with fixed length is designed. A list for the destination networks and a logical identifier for the destination hosts are used for a multicast group. The internet routing algorithm is based on these network identifiers. The mechanism incurs considerable reduction in network traffic, and reflects the characteristics of a datagram services. Consequently, it offers high robustness against network failures.