The Click Modular Router

Click is a flexible software architecture for creating routers. These routers are built from components called elements, which represent small units of router processing and are implemented as C++ objects. Click routers support both push and pull connections but with carefully specified rules as to which output and input types can be connected to explicit Queue elements.

Click runs as a single-thread in the Linux kernel and supports handlers and hot-swapping for changing configurations. It uses polling instead of interrupts and achieves a much higher max loss-free forwarding rate than Linux with interrupts. Click supports extensions such as varying types of packet schedulers and dropping policies. The Click language paired with small, modular elements makes it simple for users to create quick configurations, but a few additions would be helpful such as the use of configuration variables to prevent the user from having to copy information manually.