The present invention discloses a method for identifying node reachability, a method for identifying a link, a method for calculating a routing, and a method for disseminating node address information. In the method of the node address information dissemination, when the network is initiated, each node in the automatically switched optical network performs a node address aggregation process and an aggregation address dissemination process, and obtains and stores the aggregation address respectively. Therefore, any node in the network may judge whether the node and another node in the network are reachable to each other, and may further calculate the routing between the source and destination nodes pair. Moreover, the present invention also may determine whether any traffic engineering link in the multi-level ASON network is an external link or an internal link.