Introduction To Switch/Router Architectures

This chapter introduces the multilayer switch (or equivalently switch/router) architecture and its evolution. For the Layer 3 forwarding functions to work, the routing functions in the multilayer switch learn about other networks, paths to destination networks and destinations, through dynamic IP routing protocols or via static/manual configuration information provided by a network administrator. The Layer 3 and Layer 2 forwarding functions can each be split into subfunctions - the control plane and data (or forwarding) plane functions. In a router or switch/router, the entity that performs the control plane operations is referred to as the routing engine, route processor, or control engine. The entity that performs the data (or forwarding) plane operations is referred to as the forwarding engine or forwarding processor. From a packet forwarding perspective, the switch, router, or switch/router architectures are broadly categorized as centralized or distributed.