The exponential growth of the Information and Communication Technology (ICT) sector have led to a significant increase in energy consumption, higher electricity bills, and negative environmental and economical impacts. Several researchers, network providers, and manufacturers have been investigating different approaches to improve the energy efficiency of communication networks. Software-defined Networks (SDN) is emerging as a new networking framework that separates data plane from control plane in order to simplify network management, reduce operational costs (OPEX), and facilitate innovation. In this work, we address the centralized integral routing problem in SDN. We propose a greedy heuristic algorithm called Energy Efficient Integral Routing (EEIR) algorithm to minimize power consumption in SDN backbone networks while respecting discreteness of link rates. The performance of EEIR has been evaluated in real topologies, and compared to both optimal and shortest path solutions. Experimental results have shown a significant power saving that is as large as 44.42% can be achieved. Compared to optimal solution, EEIR provides a solution with an optimality gap in the range 7.52%- 12.67%.