The widespread deployment of Internet of Things (IoT) networks has led to revolutionary developments in multiple sectors, ensuring smooth communication across devices. RPL has emerged as a prominent and essential protocol for networks in the IoT, owing to its commendable energy efficiency and compatibility with resource-constrained devices. The Internet Engineering Task Force (IETF) has recommended the application of the routing protocol, known as RPL, for the Internet of Things (IoT) that operates on Internet IPv6, or version 6, which was created especially for lossy and low-power networks. Numerous internal and external assaults, such as rank attacks, version number attacks, worst parent attacks, and black hole attacks, may target the RPL-based network. In this study, we suggested a method for detecting and mitigating the rank attack that is based on combined and classified verification with fuzzy optimization. In three different rank attack scenarios, where the accuracy rate is 96%, energy consumption is 3456J, convergence time is 10ms and packet delivery ratio is 94%, the proposed research performs better in terms of energy usage, the quantity of control messages transmitted, the quality of service offered, and the preservation of network stability.