LoRa is one of the major communication technologies for Low Power Wide Area Networks, and a convenient technology for the Internet of Things. LoRa is usually associated with LoRaWAN, which is a protocol relying on a star network topology, in which end-nodes are connected through one-hop wireless links to one or several gateways. Despites the long range characteristics of the LoRa physical layer, physical obstacles, interferences and mobility can sometimes prevent end-nodes to communicate with gateways through single-hop links. This paper presents a new opportunistic protocol for LoRa, called LoRaOpp, that supports multi-hop communications between pairs of nodes and between nodes and gateways, even without end-to-end paths between them. This paper also presents experimental results obtained for LoRaOpp in real conditions and in emulation.