When i say Amu Darya thats where the land of Afghans begins and ends at River Jehlum.
Border of AFghanistan is upto Torkham, Tere Mangal and Chaman(the main points), beyond these 3 places, anywehre you walk will be pakistan's territory.
and as we dont see a border between pak and afghanistan,
Lets dont mix up the freedom of movement of people which is due to several factors with the term NO BORDER.