How can I find out if the trains I need require a reservation?
You can use the Interrail Rail Planner App to find out if a particular train or route requires a reservation. The Rail Planner App is a free download for iPhone and Android. On your mobile, go to the App Store (for iPhone) or Google Play (for Android) and search for Rail Planner App.
In the Rail Planner App, simply use the Trip Planner function to look up the journey you plan to take. If a reservation is required, you will see an [R] symbol and a “Reservation compulsory” notation. You can then click on the journey to see the suggested trains, where each train that requires a reservation will have the [R] symbol and “Reservation compulsory” note. The Trip Planner feature can also be used without an internet connection.