Brexit is now a reality, but as the transition period gets under way to negotiate the future trading relationship between the United Kingdom and the European Union, the situation in Northern Ireland presents an enormous challenge.

Northern Ireland will remain part of the UK customs territory, but it will also continue to align with the EU on specific trade regulations and follow EU customs rules. And many businesses which rely on cross-border trade are worried about how that will work.

Al Jazeera's Paul Brennan reports from Belfast.