A high performance scalable networking bridge/router system is based on a backbone communication medium and message passing process which interconnects a plurality of input/output modules. The input/output modules vary in complexity from a simple network interface device having no switching or routing resources on board, to a fully functional bridge/router system. Also, in between these two extremes input/output modules which support distributed protocol processing are supported. A central internetworking engine includes a shared memory resource coupled to the backbone. The architecture includes a physical layer communication system for transferring control messages and data packets across the backbone, a logical layer interprocessor messaging system which operates over the physical layer across the backbone for communication between intelligent input/out modules, and between such modules in the central internetworking engine, and distributed protocol modules which are supported on intelligent input/output modules, and communicate using the logical interprocessor messaging system with the central internetworking resources.