The transparent-bridge learning process adds entries to the bridging table based on the source address. Source addresses are never multicast addresses. Yet when examining the Catalyst bridge table, it is possible to see multicast. Why?
Some multicast addresses are identified as system addresses. For example, and frames with 01-00-0C-CC-CC-CC are directed to the Supervisor module. It is also possible to force some multicast addresses out administrator defined interfaces. This overrides the normal flooding processes.