Abstract-Today, most IP networks are still configured manually on a router-by-router basis. This is error-prone and often leads to misconfiguration. In this paper, we describe the Network Configuration Safeguard (NCGuard), a tool that allows the network architect to apply a safer methodology. The first step is to define his design rules. Based on a survey of the networking literature, we classify the most common types of rules in three main patterns: presence, uniqueness and symmetry and provide several examples. The second step is to write a highlevel representation of his network. The third step is to validate the network representation and generate the configuration of each router. This last step is performed automatically by our prototype. Finally, we describe our prototype and apply it to the Abilene network.