The Republic of Ireland's customs authorities do not have the resources to deal with a hard Brexit, a former enforcement manager has warned.
Sean Kelleher monitored the 310-mile (499km) stretch along the border from Carlingford Lough in the east to Lough Foyle in the west.
He said Revenue would be required to increase staffing to deal with "challenging" post-Brexit issues.
The UK is due to leave the EU by the end of March 2019.
The former customs manager, who served between 2007 and 2015, said commercial traffic would be subjected to certain customs controls but private vehicles should not face too much disruption.
"The reality is we will be obliged to maintain EU regulations and that will determine how those checks are carried out and to what level," Mr Kelleher told BBC news NI.
"For commercial cargo moving north to south, I would expect that all importers and exporters will register with Revenue for online declarations."
Mr Kelleher said "trade facilitation stations" should be "judicially placed somewhere near the border" to carry out checks on commercial traffic.
"You won't need too many if you are only doing a percentage check," he said. "For example, if you have traffic going west from Derry to Donegal, you may require a facilitation station, one at least in Donegal.
"For the midlands, you would need one certainly around the Monaghan border or somewhere close. For the east coast, one perhaps around the Dundalk area.
"It's all subject to what Revenue decides. They may not necessarily be in those areas but they would be the locations I would believe are where the trade facilitation stations should be located," he added.
The border separating Northern Ireland and the Irish Republic will become an EU-UK frontier after Brexit.
Mr Kelleher said he could not see a return of fixed customs posts that existed from 1923 until the creation of the EU Single Market in 1993.
"Logistically it wouldn't prove possible and politically it's unpopular," he said.
The former customs manager said "all crossings points would have to be monitored" as they would be ideal for people "with a mind to do a bit of smuggling".
He also said that random checks could be carried out by mobile patrols on crossing points and roadways along the border.
"There's going to be some disruption. It may not be major but if vehicles are called to trade facilitation stations, that's a disruption.
"It means that vehicles are going to be delayed until goods are examined and documents processed. If there are problems, the goods may be detained."
In a statement, Revenue said its focus was on facilitating trade by maximising the free flow of goods.
A spokeswoman said it was in the early stages of developing its main customs processes to cater for the phased introduction of the Union Customs Code which it said "envisages paperless customs systems, managed by electronic processing".
"The operation of customs post-Brexit and the resulting impact on business will be defined to a great extent by the terms of the agreement between the EU and the UK," she said.
"The full impacts will not be clear until negotiations have been finalised."
A series of papers is being published, including one this week covering what will happen to the border between Northern Ireland and the Republic after the UK has left the EU.
Mr Kelleher said a generation had grown up in the border region facing no checks, and would find changes difficult to accept.
"The reality is there is no border. People can drive across the land frontier and not realise they're in Northern Ireland.," he said.
"How you control that will be a major challenge for Revenue."