Abstract: This network device (300) comprises: a plurality of ports (310) which are respectively associated with a preset virtual network and a domain which configures a network on a group unit basis which differs from the virtual network; a loop detection frame transmission means (321) for transmitting a loop detection frame from the port to another device on the network; a loop detection frame receiving means (322) for receiving the loop detection frame via the port from the other device on the network; and a loop detection means (323) for detecting that a loop has occurred, on the basis of the received loop detection frame, when the transmission source of the loop detection frame is the present device, and the receiving port and the transmission source port are associated with the same domain.

Abstract: A switch apparatus providing with a loop detection function sets a port identification to a port which activates the loop detection function, only receives the loop detection frame by a high-order port in the switch apparatus connected with a backbone network or a high-order switch apparatus on the basis of the port identification set previously, and controls an inactivation of a sending source low-order port that sent the loop detection frame, when the loop detection frame is received by the high-order port.

Abstract: A switch apparatus providing with a loop detection function sets a port identification to a port which activates the loop detection function, only receives the loop detection frame by a high-order port in the switch apparatus connected with a backbone network or a high-order switch apparatus on the basis of the port identification set previously, and controls an inactivation of a sending source low-order port that sent the loop detection frame, when the loop detection frame is received by the high-order port.

Abstract: A switch apparatus providing with a loop detection function sets a port identification to a port which activates the loop detection function, only receives the loop detection frame by a high-order port in the switch apparatus connected with a backbone network or a high-order switch apparatus on the basis of the port identification set previously, and controls an inactivation of a sending source low-order port that sent the loop detection frame, when the loop detection frame is received by the high-order port.

Abstract: A switch apparatus providing with a loop detection function sets a port identification to a port which activates the loop detection function, only receives the loop detection frame by a high-order port in the switch apparatus connected with a backbone network or a high-order switch apparatus on the basis of the port identification set previously, and controls an inactivation of a sending source low-order port that sent the loop detection frame, when the loop detection frame is received by the high-order port.

Abstract: A router includes unicast protocol engines each receiving a unicast route from an adjacent node, a routing software core which stores the unicast route into trees associated with the unicast protocol engines, selects a best route among unicast routes received by the unicast protocol engines, in accordance with a priority assigned to the unicast protocol engines, and stores the best route into a best route tree, and a kernel which receives the best route from the routing software core to carry out routing control. The routing software core, when a plurality of routes addressed to a common destination is stored into the trees, registers a route retrieved by a unicast protocol engine having a highest priority, into the best route tree as a best route, applies a priority to routes retrieved by other unicast protocol engines, in accordance with a priority assigned to the unicast protocol engines, and registers the routes into the best route tree together with the best route as a best route candidate.