The click modular router

TLDR

Clicks is a new software architecture for building flexible and configurable routers. A Click router is built from packet‑processing modules called elements arranged in a directed graph, where packets flow along edges; elements perform functions such as classification, queuing, scheduling, and device interfacing, and features like pull connections and flow‑based context simplify complex configurations. Click configurations are modular and easily extendable, allowing features such as dropping policies, flow fairness, or Differentiated Services to be added with only a few elements.

Abstract

Clicks is a new software architecture for building flexible and configurable routers. A Click router is assembled from packet processing modules called elements . Individual elements implement simple router functions like packet classification, queuing, scheduling, and interfacing with network devices. A router configurable is a directed graph with elements at the vertices; packets flow along the edges of the graph. Several features make individual elements more powerful and complex configurations easier to write, including pull connections, which model packet flow drivn by transmitting hardware devices, and flow-based router context, which helps an element locate other interesting elements. Click configurations are modular and easy to extend. A standards-compliant Click IP router has 16 elements on its forwarding path; some of its elements are also useful in Ethernet switches and IP tunnelling configurations. Extending the IP router to support dropping policies, fairness among flows, or Differentiated Services simply requires adding a couple of element at the right place. On conventional PC hardware, the Click IP router achieves a maximum loss-free forwarding rate of 333,000 64-byte packets per second, demonstrating that Click's modular and flexible architecture is compatible with good performance.