A widely applied IoT routing protocol is RPL. One of the important functions of RPL in IoT is the Objective Function (OF). The OF assists in designing the Destination Oriented Directed Acyclic Graph (DODAG) structure and allows IoT nodes for network communication in terms of routing. There are several works developed for routing reliability. However, most of them lack study on reliability issues through vulnerability analysis of objective functions in RPL, especially with multiple routing scenarios.
   Most of the works in RPL are insufficient to cover all the reliability issues of smart applications. Moreover, reliable DODAG structure creation with limited packet routing delay is not implemented for IoT using the same existing security mechanism. Different OF (OF0 and MRHOF) fails in considering the security and network congestion-related metrics. So, the detection of reliable parent candidates is difficult. Incorporating the metrics for joining trusted and less congested nodes in the parent candidate list is paramount for RPL.