Unless your arrival flight and onward connecting flight is in Terminal 2 between the hours of 0400 and 1600, you will need to go landside to make your onward connecting flight. This requires that you seek permission to enter the State (you will need to have the appropriate Irish entry visa if you are visa required for entry to Ireland). Also, if you will be transiting in another airport you will need to have a  transit Irish visa.

For more information & questions, contact us or go through our frequently asked questions: Ireland Transit visa FAQs