There has been rapid growth in the number of Internet of Things (IoT) devices that produce a large volume of data such as location data, temperature data, and power usage data. These data are used in various types of services on IoT platforms. IoT services such as autonomous vehicles and factory automation system have the following three requirements. First, confidential data such as machine ID, power usage, and location information need to be locally anonymized before they are sent to a cloud server. Second, these applications require low latency response of less than 10 ms. Third, the bandwidth usage that an enormous number of IoT devices generate needs to be efficiently reduced to alleviate the burden on the cloud server. However, existing IoT platforms have limitations on the configuration of applications because most of them are cloud-based. In this study, we propose a fog-based IoT platform, where fog nodes achieve network transparency for the IoT devices and the cloud server. The network-transparent machine can be installed without modification of the existing network configuration and routing. Fog nodes transparently achieve the three requirements: anonymization of specific data in packets, real-time feedback, and reduction in the bandwidth usage.