An intra-train network management system is provided for a train having up to three or more train units. Each train unit consists of two terminal cars and zero or more intermediate cars between the terminal cars. A communications interface unit in each terminal car establishes at least two separate networks within its associated train unit. Each network connects to distinct nodes within the train unit, and the separate networks of coupled train units are crossed over. A gateway associated with each terminal car links the respective networks of separate train units coupled into a train. The network management determines the network topology by sending global device discovery messages throughout the network, and local discovery messages within each train unit that cannot penetrate the gateway(s) associated with that train unit. The local discovery messages resolve the ambiguity created by the global messages.