when one packet comes from some port of the ethernet switching, it will also check the destination address besides the source address learning.

    the ethernet switching will lookup the address-table for the destination address. if not found, this packet will be forwarded to all the other ports except the port which this packet comes in. and these ports will transmit this packet to the network it connected. if found, and the destination address is located at different port from this packet comes in, the ethernet switching will forward this packet to the port where this destination address is located according to the information from address table. but, if the destination address is located at the same port with this packet comes in, then this packet will be filtered. thereby increasing the network throughput and availability