A network system includes a plurality of lower switching hubs, and upper switching hubs connected to each of the lower switching hubs, to relay a normal frame to be transmitted and received between the lower switching hubs. Each of the lower switching hubs includes a lower switch configuring portion for configuring a first link aggregation group for all ports connected to the upper switching hub, and transmitting a first control frame containing its own identifier from all the ports connected to the one or more upper switching hubs. Each of the upper switching hubs includes an upper switch configuring portion for configuring a second link aggregation group for ports connected to a same lower switching hub, based on the first control frames received from the lower switching hubs, and transmitting a second control frame containing its own identifier from the ports configured as the second link aggregation group.