Patent ID: 8755288

Claim:
A network system, comprising: a first communication device being set up with a first address and configured to transmit and receive a frame via a port; and a second communication device connected with the first communication device using a network and being set up with a second address and configured to transmit and receive a frame using a port; a management device configured to select an object to be monitored, including a communication device and a port, and to set a time interval of transmitting of a monitor frame between the communication devices and to set a monitoring time limit using the monitor frame; wherein the first communication device includes: a monitor frame transmitter configured to, when the second communication device and a port of the first communication device are selected as an object to be monitored by the management device, generate a monitor frame including the second address as a destination address and the first address as a source address, and to output the generated monitor frame on the selected port to the network according to the time interval and the time limit; a monitoring-response frame monitor configured to, when a port of the first communication device is selected as an object to be monitored by the management device, monitor reception of a monitoring-response frame sent back on the selected port from the second communication device according to the time limit; a port configured to, when the port of the first communication device is selected as an object to be monitored by the management device, send the monitor frame using a first physical link and receive the monitoring-response frame using a second physical link; and a port controller configured to set a frame sending/receiving-enabled state as a logical status of the port on a basis of reception status of the monitoring-response frame monitored by the monitoring-response frame monitor; and wherein the second communication device includes: a monitoring-response frame transmitter configured to, in response to reception of the monitor frame, generate the monitoring-response frame by exchanging the destination address in the received monitor frame for a source address and the source address in the received monitor frame for a destination address, and output the generated monitoring-response frame to the network, when the second communication device and a port of the first communication device are selected as an object to be monitored by the management device.