Ring network and network relay device

A ring network with plural network relay devices connected in a ring shape includes first and second control ports to be transitioned into either a forwarding state that permits relaying information, or a blocking state that prohibits relaying information; and a ring protocol control unit for transmitting connection confirmation information indicative of communications being possible between the first and the second control port, from the first to the second control port, and from the second to the first control port at a predetermined time interval, or for, in the event that the first or the second control port does not receive the connection confirmation information from the second or the first control port, transmitting failure information indicative of communications being not possible between the first and the second control port, from the first to the second control port, or from the second to the first control port. The ring protocol control unit transitions the first control port into the blocking state when the first control port receives the failure information, or into the forwarding state when the first control port transmits the failure information. The ring protocol control unit transitions the second control port into the blocking state when the second control port receives the failure information, or into the forwarding state when the second control port transmits the failure information.