The IEEE 802.15.4 TSCH standard is designed to improve the reliability, timeliness, and energy efficiency of short-range wireless communications in industrial applications. TSCH relies upon a network formation process to efficiently create and maintain a synchronized reliable mesh network. The standard adopts a purely passive scan mechanism enabling joining nodes to listen to periodic Enhanced Beacons (EBs) in order to locate a TSCH network and associate to it. Nevertheless, the standard defines neither the advertisement strategy nor the rate at which the EBs should be sent. Consequently, long (re)association times might be observed, which postpones the proper functioning of the network and might have devastating consequences on the industrial application. In this paper, we propose a Fast and Active Network formation scheme (FAN) that leans on active scan procedures and Trickled beacon advertising strategies to accelerate the (re)association process. To do so, FAN equips joiners with a collision avoidance mechanism and allows them to initiate EB requests, on free channels, to trigger EBs. FAN is implemented in Contiki and evaluated through extensive realistic simulations and public testbed experiments. Obtained results assert the robustness of FAN compared to state-of-the-art solutions in terms of association times and overhead.