IoT routing layer protocol, RPL is subject to several attacks. Trust measurement schemes have been suggested to secure RPL. The trust measurement denotes how the IoT devices estimate the truth of the relationship with other devices, and it is measured as the combination of direct and indirect trust values. The trust methods are classified under three categories that are direct, indirect, and hybrid. In the first type, the nodes estimate the trust values of their neighboring nodes based on the straight communication behavioral observation. In indirect trust estimation, the nodes calculate their neighbors based on the evidence and recommendations collected from common neighbors. The hybrid model estimates the trust value of nodes by consolidating both direct and indirect trust values. Moreover, trust measurement improves the security of RPL. However, trust management is a real challenge when deploying RPL over resource-restricted tiny devices.