Routing is a two-way mechanism designed to allow formatting of external URLs so that they are more user-friendly. URL rewriting is required to allow the omission of the front controller name in the URLs of one of the applications of each project. You must use link helpers each time you need to output a URL in a template if you want the routing system to work both ways. The routing.yml file configures the rules of the routing system and uses an order of precedence and rule requirements. The settings.yml file contains additional settings concerning the presence of the front controller name and a possible suffix in external URLs.
The definitive guide of Symfony 1.2