EX3400 front-to-back fan, spare Keep your Ethernet network switches cool for proper functioning with the Juniper Fan Unit. This fan module features front-to-back airflow for efficient air inflow. With this system, the air intake happens through vents present on the front panel of the chassis while the hot air exhausts through vents present on the rear panel. The fan cooling unit is designed for use with EX Series EX3400-24P, EX3400-24T, EX3400-48P and EX3400-48T switches.