What would a no Brexit deal really mean for Ireland what would change and what would be the cost?

It would mean that Ireland and Britain grow enough balls to make their border the way they like it without reference to the EU.

Really this is all too silly! The EU cannot dictate to Britain after Brexit! Neither Britain nor Ireland wanting a Hard Border but FORCED to have one because of the EU, how ridiculous. Britain and Ireland BOTH have suddenly become regressed to infants incapable of working out their own deal, being forbidden by a paternalist EU having parental authority and control over the Irish indeed!

The fear on the island if Ireland is that it will go back to a controlled/secure border not only for trade but also for the public.... remembering that ROI/NI is a unique border of 100 yrs and totally separate from the EU( also adding the rest of the UK) with freedom of travel/ living/working but the fear is that it will kick off the troubles of the past with the IRA and terrorism and a hard /controlled border will cause untold delays with traffic as the thousands of ROI travel daily for work in NI, when there are just road works there can be 10 miles of tailbacks on the N1/A1...impossible to manage it and keep life the same as it is now

Plenty of examples of EU to non EU borders all over Europe. This fuss is being made by people who just want to throw mud at Brexit. I went across EU borders several times when visiting the Balkans. It was absolutely no problem. The lorries had to hand in paperwork about their load and passports (some EU some non EU) were scanned, all electronic.

Off the major roads there were completely unguarded small roads and paths across the borders that had been used for thousands of years, long before countries like Croatia, Serbia, Macedonia and Greece existed. I'm sure light smuggling goes that way every day. Nobody pays the slightest bit of attention,

Technology would provide the solution. Firms have already said they can process customs declarations digitally to save any delay. Neither country wants to impose a border force so it won't happen.

No Deal means a hard border.

It would mean active patrol of the border would have to beign immediately, and anyone crossing the border would need to go through proper customs processes.