Train reservation

Interrail planner shows three categories, Compulsory reservation required, Optional reservation and no reservation required (usually regional and local trains where reservation not possible).

Obviously the first cannot be avoided and there are several ways to buy them listed elsewhere,

The optional reservation category is where you use your own judgement whether you want to trust to there being spare seats on the day or want the security of a guaranteed allocated seat. A good example is the German ICE trains where no reservations are needed but some trains can get very busy. For a few euros a reservation is simple on the DB bahn site with instant e-reservation by e-mail.

Some countries trains and cross border are difficult to reserve and can be expensive.

It is very much like the lettered suburban lines of VR around HELsinki-in fact this trip is not even much longer (1 hr) and there are also trains 2 per hr. No one checks boarding, you stand if it is really full and youre too late-and are too shy to ask someone to remove bags from seat-again very much like you are likely used to already. The trip-record filled in is your ´ticket´-just as it would be when they do checks in Suomi.

Thank you for your replies! I googled the Wien-Bratislava train and noticed that it was ”train that can not be sold out”. Then I was booking a seat from Mulhouse Ville to Brussels via Strasbourg. And again you can not book a seat from Mulhouse Ville to Strasbourg in the Rail Planner App but you can book seat in SNCF website in that train. So just hope there is also room for me?

You cannot book any seat in the rail planner app. It just forwards to some of the websites where you can book, including the Interrail website.

On Mulhouse-Strasbourg, most trains are TERs and reservation is not possible. Just add the train to your pass and board. There are also a few TGV trains and for those reservation is mandatory. But the TGV is not any faster than the TER on this route.