Generally, if you have a through booking, then if you miss the flight because of the airline’s fault then you become their problem.
This doesn’t mean you’ll automatically get put on the next flight. You’ll need to talk to the airline and ask for help, and ask for re-booking. If the next flight has spare seats, then all should be well. Most likely though, you’ll get put on standby for the next flight, and hopefully will make the next one or the one after. As it’s the airline’s fault, you should get meal vouchers, help with a hotel if needed etc. (Note – the exact level of help you get depends on the jurisdiction you’re in, and the home jurisdiction of the airline)
However, if you miss the connecting flight because of your own fault (eg you fall asleep while waiting near the gate), then it’s probably no different to if you have two independent bookings….
Normally you will be put on a later flight free if you miss a connection because of a previous flight delay. I’m not sure about security and customs delays.
Credit:stackoverflow.com‘