Satellite–terrestrial networks have garnered significant attention in recent years and are extensively applied in intelligent transportation and emergency rescue. This paper provides a comprehensive review of the latest research advancements in satellite–terrestrial integrated network (STIN) technologies from a network perspective, dividing STIN technologies into three categories according to network service flows—namely, topology maintenance, network routing, and orchestration transmission technologies. Furthermore, a novel network-layer perspective is considered to examine the applications of STINs across various domains, along with related frameworks, platforms, simulators, and datasets. Finally, this paper explores the mainstream research directions in STIN technologies, with an innovative focus on the network layer. It reviews the existing literature, outlines future trends, and discusses opportunities for collaboration with related fields.