C H A P T E R 10 Exact-Match Lookups "Challenge-and-response" is a formula describing the free play of forces that pro- vokes new departures in individual and social life. An effective challenge stimulates men to creative action. -- Arnold Toynbee In Part III, for simplicity of terminology, we will generically refer to interconnect devices as routers. Each chapter in Part III addresses the efficient implementation of a key function for such routers. In the simplest model of a router forwarding path, the destination address of a packet is first looked up to determine a destination port; the packet is then switched to the destination port; finally, the packet is scheduled at the destination port to provide QoS guarantees. In addition, modern high-performance routers also subject packets to internal striping (to gain throughput) and to internal credit-based flow control (to prevent loss on chip- to-chip links). The chapters are arranged to follow the same order, from lookups to switching