A network system includes a plurality of lower switches, a plurality of upper switches, and a link group for interconnecting the plurality of lower switches to the plurality of upper switches in a multipoint-to-multipoint relationship. The link group includes a sub-link for interconnecting the plurality of lower switches to the plurality of upper switches in a point-to-point relationship as one logical link and a main link for interconnecting the plurality of lower switches to the plurality of upper switches in a point-to-multipoint relationship as one logical link. The plurality of lower switches are each set such that a broadcast frame with a broadcast address set as a destination is transmitted to the plurality of upper switches through the sub-link. The plurality of upper switches each receive the broadcast frame and resister a source address contained in the broadcast frame into an FDB of the plurality of upper switches.