Dependability is a keyword within the recent discussion about the operation of Wireless Sensor Network (WSN) as a vital part of the ever-growing Internet of Things (IoT). However, while focusing on, e.g., reliable routing it is often neglected that the energy supply is an important factor to enable dependable WSN, and thus IoT operation. Using the example of the Routing Protocol for Low power and Lossy Networks (RPL) we will show that a high operational capability is often at the expense of energy resources. Nevertheless, we will also show that this issue can be mitigated. While the resilience of RPL has been verified in a plethora of existing evaluations, the impact of simple node resets on the energy efficiency has not been investigated so far. However, resets may happen for a variety of reasons which are stated in this work as well. Thus, in the first part of this paper we examine the energy costs of resets in a RPL network. We show that such temporary node failures can have a serious impact on the network's total energy usage depending on failure location and topology. As resets are common in real WSNs this work reveals an important weakness of RPL which can even be exploited for attacks. To mitigate this issue, in the second part of this paper we propose a hardening of RPL by maintaining a backup of the RPL state information in a non-volatile memory. Improvements as well as limitations of this approach and a mechanism for a seamless recovery are discussed and described in detail. Finally, the effectiveness and the characteristics of the proposed approach to harden RPL are evaluated extensively.
