Methods, apparatus and data structures are provided for managing multicast IP flows. According to one embodiment, a network switch module includes a memory and multiple processors partitioned among multiple virtual routers (VRs). Each VR maintains a data structure containing therein information regarding the multicast sessions, including a first value for each of the multicast sessions, at least one chain of one or more blocks of second values and one or more transmit control blocks (TCBs). Each first value is indicative of a chain of one or more blocks of second values. Each second value corresponds to an outbound interface (OIF) participating in the multicast session and identifies a number of times packets associated with the multicast session are to be replicated. The TCBs have stored therein control information to process or route packets. Each second value is indicative of a TCB that identifies an OIF of the network device through which packets are to be transmitted.