Symfony2 has an in built command for building simple CRUD pages for your entities. You can use this to create simple admin pages very quickly.
The command is: php app/console generate:doctrine:crud
This will run in interactive mode giving you options on which entity to create the pages for and which pages to create (All the CRUD pages, or just the read pages).
The Configuration format option specifies (amoung other things) where the routing information is stored. I prefer to use yml so that all of my routing information is together.