An arrangement and method for implementing multicasting in IP networks, in which multicast packets are transmitted along a multicast tree from one transmitter through several multicast controllers to several recipients is discussed. In the method at least one multicast tree intended for control messages is generated in the network from a network multicast controller to cell-level multicast controllers. The network multicast controller transmits along the multicast tree control messages to the cell-level multicast controllers. The control messages contain information on the network multicast and a command to connect to the network multicast tree intended for multicasts.