Less than 2 hours
Belfast City Airport to Dublin Airport is about 85 miles.
Roughly 2 hours.
Dublin Airport in Dublin. Cork Airport in Cork. George Best Belfast City Airport in Belfast.
About 97 miles or 157 kilometres.
What you would do is get to the Europa Bus Centre, the main bus station in Belfast. From there you can a bus every hour, on the hour to Dublin. Just check that it does stop off at Dublin Airport, as some of them may not do.
Dublin is bigger than Belfast.
Belfast is serviced by 2 airports. Belfast International airport is a 40 minute bus Journey away from the city centre and Belfast City airport is a 20 minute bus journey away. Buses are frequent and reasonably inexpensive. Taxi's are also readily available from each airport
Yes, you can get buses from Dublin Airport to Belfast.
It depends on what you mean by "major" (most departures, most passengers enplaned, most destinations, most international destinations). Generally speaking, though, the top three would probably be Dublin, followed by Belfast (City and International), and Shannon.
30-50 mins approx, depending on the time of day you go.
George Best Belfast City Airport.
It is from Belfast City Airport.