From ideal outcome to worst-case scenario
No Change: Foreign Affairs Minister Charlie Flanagan says keeping the current situation, where there are no customs or identity checks on the border, is the ideal outcome for everyone in Ireland and Britain. But that will be hard to achieve. Britain would need to make concessions on immigration to get full EU single market access.
A 'hard border': That would see customs and security huts in Armagh, Fermanagh, Tyrone and Derry. It would be back to the bad old days and absolutely the worst of all options. However, it cannot be ruled out, if compromises are not reached.
Pulling back the border to Britain: This would allow an almost non-existent border between Ireland north and south. But it would raise the prospect of checks on people landing in Britain, possibly for people coming from both the Republic and the North.
A Virtual border: This would involve deploying video and computer technology to track those crossing the border for security and/or customs purposes. The details have to be worked out. The plus is no security posts. The minus is that it may be just a futuristic version of the old 'hard border'.