<div>Internet of Things (IoT) is one of the fastest emerging networking
paradigms enabling a large number of applications for the benefit of
mankind. Advancements in embedded system technology and compressed IPv6
have enabled the support of IP stack in resource constrained
heterogeneous smart devices. However, global connectivity and resource
constrained characteristics of smart devices have exposed them to
different insider and outsider attacks, which put users’ security and
privacy at risk. Various risks associated with IoT slow down its growth
and become an obstruction in the worldwide adoption of its applications.
In RFC 6550, the IPv6 Routing Protocol for Low Power and Lossy Network
(RPL) is specified by IETF’s ROLL working group for facilitating
efficient routing in 6LoWPAN networks, while considering its
limitations. Due to resource constrained nature of nodes in the IoT, RPL
is vulnerable to many attacks that consume the node’s resources and
degrade the network’s performance. In this paper, we present a study on</div>


<div>various attacks and their existing defense solutions, particularly to
RPL. Open research issues, challenges, and future directions specific to
RPL security are also discussed. A taxonomy of RPL attacks, considering
the essential attributes like resources, topology, and traffic, is shown
for better understanding. In addition, a study of existing cross-layered
and RPL specific network layer based defense solutions suggested in the
literature is also carried out.</div>