As Figure 1 shows, the availability of high bandwidth access technology for today's Internet customers and high bandwidth access to the Internet together create a potential throttle point when routing traffic from customers to the Internet. Riverstone Networks Layer 3 Switch Router architecture alleviates the problem by completely separating the background task of generating the route tables, and the real-time task of processing the packet to create flow information. This is accomplished through Distributed Hardware Routing. Riverstone's unique method of distributing the routing tables to each line card allows the line card to make real time forwarding lookups as the first packet in a stream arrives and then send it directly to the best next hop on the way to its ultimate destination. The ever-changing packet flow of the Optical Metro Backbone is transported at wire speed without taxing the Riverstone Switch Router.
Software routers process every packet coming through the router using the CPU on the control module.
Along with the packet processing, the control module would also perform all routing protocol functions, and create and maintain the tables used to make the routing decisions on the packet. When the access and aggregation rates were relatively low speed, the limitations of software based routers were tolerated. Hardware-assisted routers speed up the process greatly by splitting the functionality. At the same time that the packet is being forward, the control module writes the forwarding information for the flow into the ingress line card along with any Quality of Service and access control policy information associated with the flow. When subsequent packets arrive, the ASICs on the line card look to see if the forwarding information is available locally and sends the packet along based on the forwarding and policy information that the control module wrote into the line card's memory.