Nowadays the data service is increasing explosively . In order to meet the need of more bandwidth and higher service quality

the optical network will grow more and more intelligent . The technology of Automatically Switched Optical Network （ASON） which is put forward recently presents the direction of optical network development.

hence becomes the research focus of the next generation optical network architecture . Because of the connection-oriented character of ASON

the hierarchical routing technology is introduced to the ASON network for better scalability and flexibility. The routing procedure is simplified by topology abstraction and aggregate routing information . Through the hierarchical routing architecture

operators can shield the internal detail of their optical network and configure the network arbitrarily

which will improve the network security greatly and will guarantee better scalability and flexibility . In this paper

the architecture of ASON hierarchical routing is depicted deeply together with the requirement by hierarchical routing to the inter-domain interface . We also introduce the Domain to Domain Routing Protocol （DDRP） in detail that is fit for the ASON hierarchical routing . At last we discuss the networking scheme for ASON hierarchical routing based on DDRP .