Click is a new software architecture for building flexible and configurable routers. It consists of packet processing modules called elements, which can be combined to form a router configuration as a directed graph. The architecture supports push and pull connections, flow-based router context, and explicit packet storage through the Queue element. Click configurations are written in a simple language that allows for easy manipulation and extension. The Click IP router, implemented on general-purpose PC hardware, achieves a maximum loss-free forwarding rate of 333,000 64-byte packets per second, demonstrating its performance and modularity. The paper also discusses the kernel environment, performance evaluation, and related work.Click is a new software architecture for building flexible and configurable routers. It consists of packet processing modules called elements, which can be combined to form a router configuration as a directed graph. The architecture supports push and pull connections, flow-based router context, and explicit packet storage through the Queue element. Click configurations are written in a simple language that allows for easy manipulation and extension. The Click IP router, implemented on general-purpose PC hardware, achieves a maximum loss-free forwarding rate of 333,000 64-byte packets per second, demonstrating its performance and modularity. The paper also discusses the kernel environment, performance evaluation, and related work.