  Low-Power and Lossy Networks (LLNs) run on resource-constrained devices and
play a key role in many Industrial Internet of Things and Cyber-Physical
Systems based applications. But, achieving an energy-efficient routing in LLNs
is a major challenge nowadays. This challenge is addressed by Routing Protocol
for Low-power Lossy Networks (RPL), which is specified in RFC 6550 as a
"Proposed Standard" at present. In RPL, a client node uses Destination
Advertisement Object (DAO) control messages to pass on the destination
information towards the root node. An attacker may exploit the DAO sending
mechanism of RPL to perform a DAO Insider attack in LLNs. In this paper, it is
shown that an aggressive attacker can drastically degrade the network
performance. To address DAO Insider attack, a lightweight defense solution is
proposed. The proposed solution uses an early blacklisting strategy to
significantly mitigate the attack and restore RPL performance. The proposed
solution is implemented and tested on Cooja Simulator.
