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The Click modular router

Eddie Kohler, Robert Morris, Benjie Chen, John Jannotti, and M. Frans Kaashoek

Abstract

Click 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, queueing, scheduling, and interfacing with network devices. A router configuration 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 driven 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 sixteen elements on its forwarding path; some of its elements are also useful in Ethernet switches and IP tunneling configurations. Extending the IP router to support dropping policies, fairness among flows, or Differentiated Services simply requires adding a couple elements 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.

In ACM Transactions on Computer Systems 18(3), August 2000, pages 263-297. (BibTeX entry)

This paper is a revised and expanded version of our SOSP paper, which appeared in the Proceedings of the 17th ACM Symposium on Operating Systems Principles (SOSP '99), Kiawah Island, South Carolina, December 1999, pages 217-231. Compared to the earlier paper, it has improved explanations of basic concepts, more detail, more examples, and significantly better performance results.