A method and apparatus for authorizing forwarding states in a Layer 2 device of a multicast system includes a forwarding table for use in forwarding communications to group members over interfaces of the Layer 2 device. According to one aspect of the invention, associated with the forwarding state is an authorization flag. The authorization flag signals whether or not the forwarding state is an authorized forwarding state over which multicast communications may be transferred. The Layer 2 device snoops authorization communications between a host and a layer 3 device, and updates the forwarding table authorization flags in response to these communications.