In a network including a plurality of nodes, a node transmits data to another node, receives data from another node, and stores a communication history between a plurality of other nodes and the node itself. When an acknowledge response to data transmitted to a first node among the plurality of other nodes is not received, the node generates a duplicate data of the transmitted data. When a duplication report indicating detection of duplicate data transmitted to a second node among the plurality of other nodes has been received from one of the plurality of other nodes, the node refers to the communication history, and identifies the first node as a cause of generation of the duplicate data. Thereafter, the node generates a check request that include a communication history between the first node and the node itself and that requests the first node to check the communication history.