[1][2] Vietnamese National Route 1 starts at the border near this pass, which lies less than 5 km north of the town of Đồng Đăng in Lạng Sơn province, ending in Năm Căn in Cà Mau province.

Traditionally, the pass served as the exact border between China and Vietnam,[1][2] hence there is also a Vietnamese historical saying: "Nước Việt Nam ta trải dài từ Ải Nam Quan đến mũi Cà Mau,"[3][unreliable source?

translated as "The Vietnamese nation stretches from Ải Nam Quan to Cape Cà Mau".

However, since the Franco-Qing Convention of 1887, the border has been determined to be south of the Pass itself, putting it entirely within Chinese territory,[5] in Pingxiang, Chongzuo County, Guangxi Autonomous Region,[6] and the official border between the two nations is beyond this pass.

18 was erected and represented on an 1894 map to be "along the road from Đồng Đăng to Nam Quan", but has since been lost.