RPL (Routing Protocol for Low Power and Lossy Networks) has been designed for low power networks with high packet loss. Generally, devices with low processing power and limited memory are used in this type of network. IoT (Internet of Things) is a typical example of low power lossy networks. In this technology, objects are interconnected through a network consisted of low-power circuits. Example IoT applications are smart energy grid, smart home, connected car, intelligent transport systems, and smart cities. IoT is different from many similar technologies due to the existence of low power electronic circuits and limited connectivity. Information security is one of the main IoT concerns. The emergence of new types of security vulnerabilities in IoT devices and the escalation of their damages through numerous IoT applications is considered a major deployment drawback for RPL. In this paper, major cyberattacks against RPL, as well as related security solutions are addressed. Then, these solutions are classified and their weaknesses and strengths are investigated. Finally, it discusses the state-of-the-art status of information security in RPL.