One embodiment of the present invention provides a switch. The switch comprises one or more ports, a link management module and a load balancing module. The link management module operates a port of the one or more ports of the switch in conjunction with a remote switch to form a virtual link aggregation. The load balancing module generates an index of a weight distribution vector based on address information of a multicast group associated with the virtual link aggregation. A slot of the weight distribution vector corresponds to a respective switch participating in the virtual link aggregation. In response to the index indicating a slot corresponding to the switch, the load balancing module designates the switch as primary switch for the multicast group, which is responsible for forwarding multicast data of the multicast group via the virtual link aggregation.