This application provides a node device implementing connection establishment for a Space Division Multiplexing (SDM) network. A first node receives a path (Path) message, which includes a plurality of label objects, each label object includes a field used to indicate a number of an optical core in a multi-core optical fiber, and idle spectrum information of each optical core. The first node then obtains an intersection set of the idle spectrum information of each optical core indicated in the path message and idle spectrum information of a corresponding optical core on a first link. The first node sends, over the first link, a path message that carries an intersection set result, where the first link is a link between the first node and an adjacent node in a direction from the first node to an end node.