Nowadays, power consumption reduction techniques are being increasingly used in computer systems, and high-performance computing systems are not an exception. In particular, the power consumed by the interconnect circuitry has a non-negligible contribution to the total system budget. In this scenario, fat-tree interconnection networks are one of the most popular topologies. This topology is particularly well-suited for applying power consumption reduction techniques since it provides multiple alternative paths for each source/destination pair. In this paper, we present a mechanism that dynamically adjusts the available network bandwidth by switching links on and off, according to the traffic requirements. This mechanism provides significant reduction in power consumption while maintaining the original underlying routing algorithm, at the expense of slight latency increase for low loads.