The existing research on the Internet of Things(IoT) security mainly focuses on attack and defense on a single protocol layer. Increasing and ubiquitous use of loT also makes it vulnerable to many attacks. An attacker try to performs the intelligent, brutal and stealthy attack that can reduce the risk of being detected. In these kinds of attacks, the attackers not only restrict themselves to a single layer of protocol stack but they also try to decrease the network performance and throughput by a simultaneous and coordinated attack on different layers. A new class of attacks, termed as cross-layer attack became prominent due to lack of interaction between MAC, routing and upper layers. These attacks achieve the better effect with reduced cost. Research has been done on cross-layer attacks in other domains like Cognitive Radio Network(CRN), Wireless Sensor Networks(WSN) and ad-hoc networks. However, our proposed scheme of cross-layer attack in IoT is the first paper to the best of our knowledge. In this paper, we have proposed Rank Manipulation and Drop Delay(RMDD) cross-layer attack in loT, we have investigated how small intensity attack on Routing protocol for low power lossy networks (RPL) degrades the overall application throughput. We have exploited the Rank system of the RPL protocol to implement the attacks. Rank is given to each node in the graph, and it shows its position in the network. If the rank could be manipulated in some manner, then the network topology can be modified. Simulation results demonstrate that the proposed attacks degrade network performance very much in terms of the throughput, latency, and connectivity.