Increasing connectivity of almost all things through the internet without any human intervention, namely, IoT, is a major trend today. To allow interactions among the things, wireless networks are being used invariably, and thus routing plays a vital role. An IPv6 based Routing Protocol for Low-Power and Lossy Networks (i.e. RPL) is given by IETF RoLL working group as a cornerstone for efficient communication among resource-constrained devices. RPL employs a hierarchical structure called Destination Oriented Directed Acyclic Graph (DODAG), making it suitable for both small scale and large scale LLN deployment. The trickle timer and objective function are the main components of RPL, which help to regulate control messages and determine the most efficient path respectively. Constraint nature of LLN leads to optimize the routing algorithm w.r.t. route discovery, route establishment, energy efficiency, network topology, scalability, reliability, latency, and error-free data transfer to the destination. This comprehensive survey focuses on a thorough examination of various RPL-based routing protocols ranges from the different routing metrics to the most recent routing solution. In this context, we also encompasses a diverse array of RPL variants, extensions, and optimizations, exploring their unique contributions, functionalities, and performance characteristics. Through an exhaustive review of existing literature and implementations, this survey aims to provide a comprehensive understanding of the evolving landscape of RPL routing protocols. The insights gleaned from this survey are poised to guide researchers, practitioners, and network architects in making informed decisions for the deployment and optimization of RPL-based solutions, ensuring robust and resilient communication in low power and lossy IoT environments.