As already mentioned, [the Durand Line] cuts tribes and tribal groups in half. The Birmal tract of Waziristan is on the Afghanistan side, with the rest of Waziristan on the British or Pakistani side. The Mohmand tribal areas are also cut in two. And, inevitably, because the border is generally in a very distant set of areas, it is highly porous and difficult to police, especially when family groups are on both sides.
Bijan Omrani, “The Durand Line: History and Problems of the Afghan-Pakistan Border,” Asian Affairs