Normally you shouldn't need any routes, as the default for the URI is: controller/method/any/params/you/want/to/pass.
You do need a route if you want the page number to be the second URI segment, which by default is reserved for the action method name.
Which route you need depends on how you created the controller. If your action_index deals with pagination, you can route to 'product/index' or 'product' (which defaults to 'index'), both work fine.