Why userspace rather than writing kernel space modules?

Hi everyone, I'm a newbie to BIRD who ran across it from freshmeat.net. Being a newbie, I have some newbie questions. How efficient is it to sync with kernel space routing tables if the routing tables change rapidly? How often does a routing table change with a typical server configuration and typical server traffic? Lastly besides the portability, why implement a userspace daemon that is required to sync with the kernel when kernel space modules could be written to directly manipulate the routing tables themselves? Thanks for answering these questions. Currently, I am EXTREMELY interested in this project, and would like to potentially put some development time into BIRD. Daniel Holmlund --