How can I sell custom web server control over Internet

[FastCode]

I wish to make some custom web server controls, and sell it over Internet. How to protect my work and controls from copying? It will exist two type of licence: per domain and per server. How to find what is domain of ASP.NET page where my control is running, or what is IP adress of the web server?
Also, anyone know for some article or tutorial about this subject?
How others companies solved this problem?