This paper presents two lightweight mitigation techniques for RPL Version Number Attacks (VNA) which affect the performance of IPv6-connected Low Power and Lossy Networks (LLNs) detrimentally. In RPL VNA, an attacker maliciously changes the version number of the network and thus increases delay and control message overhead and reduces network lifetime and packet delivery ratio. Simple yet effective mitigation mechanisms proposed in this paper promise significant performance improvements in an RPL network under attack. By means of the proposed techniques, the delay caused by the attacker can be shortened up to 87%, the average power consumption can be reduced up to 63%, the control message overhead can be lowered up to 71% and the data packets delivery ratio can be increased up to 86%. The proposed techniques, while allowing the ordinary RPL operation, trade off the mitigation performance against the resource overheads and thus allow network administrators to choose the right scheme for their RPL network. (C) 2018 Elsevier B.V. All rights reserved.