New Long-Range radio technologies have recently emerged in the IoT landscape. These technologies work in the Sub-GHz bands, allowing low-power communications over long distances. They are typically based on star-topology networks, where nodes send the data directly to a base station connected to the Internet. One of such technologies is LoRa. Enabled LoRa-based multihop communications would open up new possibilities. In this paper we present a solution allowing to have multihop LoRa communications. This is done by means of a newly designed MAC protocol (RLMAC), used to select the Spreading Factor for each available neighbor. The proposed Objective Function used by RPL will therefore be able to select the routing path that minimizes time on-air. By selecting the path with the lowest time on-air, the power consumption can be decreased, enlarging network lifetime. Preliminary validation tests are also presented in the paper.