LPWAN technologies are playing a major role in the IoT scenario due to their extensive radio range, use of free frequency bands, and low energy consumption. Among these technologies, longrange WAN (LoRaWAN) transmits through several kilometers with data rates up to 5.5 kb/s, making it useful for applications such as smart city monitoring, precision agriculture, and environmental tracking. However, LoRaWAN supports only one-hop communication between end nodes and gateways. Because links can be kilometers long, LoRaWAN signals may encounter obstacles or interference, affecting packet reception. Therefore, different studies have proposed using routing schemes to create multihop communication and improve LoRaWAN performance. The article has the following contributions: first, we present the main approaches to build multihop communication in LoRa networks. Second, we summarize different routing protocols proposed for the technology. Finally, we describe different challenges to improve the performance of routing protocols for LoRaWAN.