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[Inziladun]

Originally Posted by Morthoron

Well, the vale was indeed protected by a Ring of Power, so certainly a 'girdle' meant to confuse and hinder enemies makes sense. Galadriel as well protected Lothlorien in the same manner, confounding Sauron's attempts to discover the movements and thoughts of the Wise.

It's fairly clear to me Vilya was the primary protection of Rivendell. I wonder though, just how its influence (and Nenya's also) kept out unwelcome intruders.
Was it something along the lines of only those dwelling there with the wielder of the Ring being able to penetrate the barrier (and bring outsiders with them) under ordinary circumstances, and 'exceptions', such as Bilbo, Boromir, Legolas, Glóin and Gimli having to have special conscious permission of the Ring's master to enter?