Ever since Internet of Things (IoT) has become a reality, fresh challenges have been propping up in a day-to-day manner for keeping the paradigm robust. As an IoT enabling technology, Low Power Lossy Networks (LLNs) play a notable role in ensuring the connectivity of devices, and thereby the efficient functioning of applications. Considering their resource constrained nature, routing protocols designed for LLNs demand a proper management of vital resources. The paper considers node memory, node

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... battery, and network bandwidth to be vital network resources, and reviews in detail the existing LLN routing protocols as well as routing metrics with respect to the level of resource management achieved by each of them. Finally, the paper enlists research challenges in the field of LLN routing, which can be considered as the need of the hour, for assisting the IoT paradigm to reach its maximum potential.