An extra traffic is transmitted in a redundant communication network using a backup path. A working communication path and the backup communication path connect two switching nodes. A switching control packet including information representing whether a first traffic passes through the working communication path is transmitted between the two switching nodes via the backup communication path. Under normal conditions, the first traffic passes the working communication path. A backup node that has received the second traffic from outside the backup communication path, determines whether the first traffic is passing through the working communication path based on information included in the switching control packet. If the first traffic is passing through the working communication path, the backup node transmits the second traffic to another backup node along the backup communication path.