Provided is a method of controlling a network concentrator 100 which controls a link status between, of a plurality of ports 102, 104, 106, 108, at least one port 102, 104, 106 that belongs to a first group 10 and at least one port 108 that belongs to a second group 12 corresponding to the first group 10. The method comprises the steps of: detecting that each of the ports that respectively belong to the first group 10 and the second group 12 is link-up or link-down; and as a result of the detection step, if at least one port in one group of the first group 10 and the second group 12 is link-up and all the ports in the other group are link-down, setting the link-up port in the one group to disablement.