Jamieson-Fausset-Brown on Numbers 34:10
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.
John Gill on Numbers 34:10
And ye shall point out your east border from Hazarenan to Shepham. From the place where the northern border ended, which Jerom says (u) the Hebrews call Apamia, as both the Targums of Jonathan and Jerusalem do here. Shepham was a city between Hazarenan and Riblah in the tribe of Naphtali, where Adrichomius (w) places it.
(u) Comment. ut supra. (cf. ver. 15.) (w) Theatrum Terrae Sanct. p. 114.
John Calvin on Numbers 34:1-12
And the Lord spake unto Moses. God here undertakes the office of a prudent and careful father of a family, in fixing the boundaries of the land on every side, lest their right to posses it should ever be called in question. He begins on the southern side, where it must be observed that the district of Bashan is included in it, and all that the Israelites had acquired before their passage of the Jordan, so that this addition was approved of by God. He extends this part as far as the wilderness of Sin, and the borders of Edom, and brings it round from Kadesh-barnea to Addar, and the passage of Azmon, and, finally, to the stream which washes [228] the city of Rhinocorura, in the immediate vicin…
Read the whole note in the consoleKeil & Delitzsch on Numbers 34:10-12
The Eastern Boundary. - If we endeavour to trace the upper line of the eastern boundary from the fountain-place just mentioned, it ran from Hazar-enan to Shepham, the site of which is unknown, and "from Shepham it was to go down to Riblah, on the east of Ain" (the fountain). The article הרבלה, and still more the precise description, "to the east of Ain, the fountain, or fountain locality" (Knobel), show plainly that this Riblah is to be distinguished from the Riblah in the land of Hamath (Kg2 23:33; Kg2 25:21; Jer 39:9; Jer 52:27), with which it is mostly identified. Ain is supposed to be "the great fountain of Neba Anjar, at the foot of Antilibanus, which is often called Birket Anjar, on ac…