Jamieson, Fausset and Brown on Numbers 34:10-12

10-12. east border--This is very clearly defined. Shepham and Riblah, which were in the valley of Lebanon, are mentioned as the boundary line, which commenced a little higher than the sources of the Jordan. Ain is supposed to be the source of that river; and thence the eastern boundary extended along the Jordan, the sea of Chinnereth (Lake of Tiberias), the Jordan; and again terminated at the Dead Sea. The line being drawn on the east of the river and the seas included those waters within the territory of the western tribes.