Vehicles in formation often lack global information regarding the state of all the vehicles, a deficiency which can lead to instability and poor performance. In this paper, we demonstrate how exchange of minimal amounts of information between vehicles can be designed to realize a dynamical system which supplies each vehicle with a shared reference trajectory. When the information flow law is placed in the control loop, a separation principle is proven which guarantees stability of the formation and convergence of the information flow law regardless of the information flow topology.