Abstract The huge development of Packet Switching Data Network (PSDN) based on a large number of nodes, and in many cases, with different capabilities, has made necessary to have an automatic tools to help the planner in the design of large PSDN. The aim of this paper is to present NETPLAN: a Rule Based System to design the PSDNs architectures and their topological layout, to plan the needed resources, to choose and verify proper routing strategy and to obtain an optimized network.