This application describes a data transmission method, a network node, and a storage medium for communications technologies. In this application, an underlay segment identifier corresponding to an underlay path is designed, and the underlay segment identifier is advertised, so that a node on a segment routing network can sense the underlay path by using the underlay segment identifier. In this way, when a data packet is transmitted, the data packet can be sent based on an underlay segment identifier carried in the data packet and through an underlay path corresponding to the underlay segment identifier. Therefore, an underlay path through which a data packet is to be transmitted may be specified based on a service requirement, so that different data packets can be transmitted through different underlay paths, thereby improving flexibility and facilitating traffic planning.