In next-generation IP over WDM networks, lightpaths are set up or torn down dynamically. Traditionally, OSPF in IP layer and OSPF-TE in optical layer disseminate routing information independently. Obviously, this 2-layer routing mechanism is complex and O&M cost is high. Furthermore, in a dynamic environment, both OSPF-TE and OSPF have very heavy control overheads when lightpaths change frequently. In this paper, an integrated routing protocol is proposed. The link state information of both IP layer and optical layer is disseminated simultaneously using the same routing protocol messages. The proposed protocol also advertises wavelength availability information if necessary in order to reduce the blocking probability of routing and wavelength assignment (RWA) algorithm. This proposed integrated protocol is very simple. Furthermore, its control overhead can be reduced from several to about ten times. In addition, RWA's performance is also improved. Hence, the performance of the IP over WDM networks will be improved greatly and significantly.