Route the url

[eluser]Volkscom[/eluser]
There is any function used to route the url in CodeIgniter?.
I have a contoller 'prdt_det' and 'disp_det' method and the product id as a parameter.
www.hello.com/index.php/prdt_det/disp_det/__2__3.In this I need to check if the parameter contains only numbers and '_'.How can I set this?.