We consider the power-efficient design of an Internet Protocol (IP)-over-Wavelength Division Multiplexing (WDM) network, tackling the problem of deciding which equipment needs to be installed in both the optical and IP layer. Our model explicitly targets the minimization of cost considered as either Capital Expenditures (CapEx) or power. In contrast to the models already presented in the literature, we take into account routing constraints and consider a comprehensive set of realistic scenarios defined by a network topology, traffic, cost and power values of network devices in both layers. Results indicate that the introduction of realistic constraints and parameters still allows power-efficient networks to be designed. The total power consumption in the considered network scenarios is at most 26.5% higher than when using previous models.