This question already has an answer here:
Suppose I have an itinerary A - C with 1 stop at B, booked under a single ticket number on the website of airline X, where the leg A - B is operated by airline Y and B - C is operated by X.
If the flight A - B is delayed to a point where I miss my connection, whose responsibility is it to see that I'm fed, watered, and eventually delivered to destination C? Is it Y or X?
Apart from an academic interest in the answer, I'm going to be travelling on such an itinerary soon, and would like to known with whom I should be having a polite but firm conversation in case things go wrong. In my particular scenario, the leg B - C is only operated a few times a week, not daily, so a missed connection would be quite inconvenient.