Internet Engineering Task Force (IETF) has recommended the use of routing protocol for Low Power and Lossy Network (RPL) for Internet Protocol version 6 (IPv6) enabled Internet of Things. However, RPL is vulnerable to internal and external attacks in a network. A malicious node in a rank attack, which is consumed by its child nodes, advertises false rank information. This consequently causes the selection of a malicious node as preferred parent for routing information to the sink node. Given the widespread application of RPL protocol in smart homes, smart cities, and the smart world, it is imperative to address this problem. In this paper, a novel Sink-based intrusion detection system (SBIDS) for the detection of rank attack in RPL is presented. SBIDS has less computational overhead as all detection processes take place at the sink node, which saves network resources. Through a comprehensive simulation analysis, it is shown that the proposed SBIDS provides high detection rate.