a method and apparatus for accomplishing source learning in a data switch of the type having a plurality of switching modules where each supports one or more external network devices and a backplane interconnecting the switching modules . each switching module has logic resident thereon for performing distributed source learning , including configuring unknown source addresses “ seen ” in inbound packets and for notifying the other switching modules that such source addresses were “ seen ” on a port thereof . address - port associations are thereby configured on the switch using distributed logic , i . e . without intervention by a centralized management entity . in regard to configuring destination addresses — when a destination address is unknown , packets are delivered over a multicast queue until the destination address is found . once the destination address is found , a method of flow integrity is used to avoid out of order packet delivery when the device transitions from using a multicast flood queue to a unicast queue .