Redirecting a function included in an operating system is disclosed. The redirecting is achieved by identifying an original function call in a kernel and replacing the function call with a replacement function call so that the replacement function is called in place of the original function. In this way the original function call is bypassed and the original call is redirected to the replacement function. This may be done to augment or replace the original function. In one embodiment, when a packet is received, a replacement receiving function is called in place of the network receiving function that was provided with the kernel. In this way, different, less or additional processing of received packets may be performed.