The wave of IoT is also on the rise worldwide. In terms of IoT network, various security concerns have been pointed out, especially when places and things previously that had been completely separated are to connect to a general business LAN or the external Internet. Whether you are already deploying IoT network or are planning to introduce them, network administrators need to take measures for network security including policy management when implementing IoT.In this seminar, based on the introduction of "Flowmon", a network visualization and diagnostic product using NetFlow, we will propose a simple and effective solution for future trends that will start soon.