Interactive (a.k.a. push and shove) routing is a key feature of advanced PCB design software, greatly reducing the time it takes to design and modify the board. There is however no literature on the subject available. The presentation will focus on the internals of the router implemented by CERN for the Kicad PCB editor: - efficient routing geometry storage and obstacle detection, - shove & hug algorithm based on octagonal primitives and force propagation, - optimization and trace smoothing techniques, - length tuning and differential pair routing.