  Driven by the special requirements of the Lowpower and Lossy Networks (LLNs),
the IPv6 Routing Protocol for LLNs (RPL) was standardized by the IETF some six
years ago to tackle the routing issue in such networks. Since its introduction,
however, numerous studies have pointed out that, in its current form, RPL
suffers from issues that limit its efficiency and domain of applicability.
Thus, several solutions have been proposed in the literature in an attempt to
overcome these identified limitations. In this survey, we aim mainly to provide
a comprehensive review of these research proposals assessing whether such
proposals have succeeded in overcoming the standard reported limitations
related to its core operations. Although some of RPL weaknesses have been
addressed successfully, the study found that the proposed solutions remain
deficient in overcoming several others. Hence, the study investigates where
such proposals still fall short, the challenges and pitfalls to avoid, thus
would help researchers formulate a clear foundation for the development of
further successful extensions in future allowing the protocol to be applied
more widely.
