Over the last 50 years, we’ve made a lot of progress in developing the Internet from a tiny interconnection of a handful of computers to a worldwide fabric with billions of nodes. During that journey, we’ve learned an enormous amount about how to build networks and the routers that interconnect them. The mistakes that we all made generated some important lessons along the way, for those that chose to learn them.
In the beginning, routers were simply generic computers, with Network Interface Cards (NICs) attached to a bus.
Figure 1 Network interface cards attached to a bus.
This works to a point. In this architecture, packets enter a NIC and are transferred by the CPU from the NIC into memory. The CPU makes a forwarding decision and then pushes the packet out to the outbound NIC. The CPU and memory are centralized resources, bound by what they can support. The bus is an additional limitation: the bandwidth of the bus must be able to support the bandwidth of all of the NICs si