Low-power and Lossy Networks (LLN) are sensors with limited energy and resources. Sensors deployed in application environment generate large amounts of data. Routing the data with high reliability is a challenging one in LLN. Routing Protocol for Low-power and Lossy Networks (RPL) is the routing protocol designed for the Internet of Things (IoT). RPL selects the route based on the objective functions - Objective Function zero (OF 0) and Minimum Rank with Hysteresis Objective Function (MRHOF). The real-time application environment Industrial Internet of Things (IIoT) was considered for this proposed work. The routing protocol used in the real-time reliable environment should route the data with high reliability, so in this proposed work a new objective function Residual Energy based Expected Transmission Count (RE-ETX) is designed for the reliable environment. The objective function RE-ETX was applied to the static and mobile IIoT environment. The RE-ETX is compared with the different objective functions. The results show that the RE-ETX has improved the packet delivery ratio by 6–9% and latency was decreased by 1–3%, hence RE-ETX helps in preserving reliability of the network.