A communication network system includes a processor, and a plurality of node apparatuses using a protocol to establish paths therebetween, wherein the processor determines each of the node apparatuses to be a packet source or a packet destination, and operates to detect an occurrence of failure in two paths being established between the packet source and the packet destination in the communication network system, and wherein the processor transmits packet data including user data through one of the two paths, and when one of the node apparatuses detects an occurrence of a failure in one of the two paths, the processor changes the path to the other path.