Layover in Frankfurt for 1h40m - is it enough? What happens otherwise? – travel.stackexchange.com

I'm not sure if this is still true, but I remember that I once realized that there was no airside connection from terminal A/B to C, which means that you will also have to pass through security, further cutting into your time.

Also, the smaller aircraft more often get outfield parking positions, then you will be bussed to the terminal, which also takes more time than getting off via a jetway (on my last connecting flight from FDH, it was 30 minutes between touchdown and actually reaching the terminal building. Consider that the maximum, the plane was parked at the very end of the airport grounds).

As the others have mentioned, Lufthansa will rebook you if you miss the connection, but given that there is only one direct flight to Chennai every day, I would rather try to get an earlier flight into Frankfurt.

Depending on where you are staying the night before your travel, and how you will be getting to the airport, it might be worth taking the train instead of a connecting flight: it gives you much more flexibility, plus the train ride from Stuttgart main station to Frankfurt airport is roughly one hour, while the ride to Stuttgart airport takes about 30 minutes; so heading straight to Frankfurt airport is actually faster.