The authors are concerned with the design of multilayer architectures in distributed systems and computer networks. First, they give the basic knowledge that any designer must have for designing, in a consistent way, a set of layers. This knowledge concerns the objects of a layer, their attributes and their relationships. Second, they consider an example of network interconnection, at the network layer, on the basis of the internal organization of the network layer defined by ISO and apply this basic knowledge for specifying the architecture for internetworking.>