In this paper, we study the problem of designing propagation protocols for network-wide localization based on two-way ranging. At the beginning, a network contains a few localized anchor nodes and a large number unlocalized nodes. Unlocalized nodes in the communication range of anchor nodes perform two-way ranging, estimate their positions, and become anchor nodes. The process repeats until all nodes know their positions. We consider three protocols for this propagation process, analyze their convergence speed, and evaluate the communication costs related to the energy consumption. We show that the proposed Optimized Beacon protocol requires much less messages than two other considered protocols while achieving almost the same convergence delay as the Beacon protocol.