This read-write value indicates whether a stack's External ID has been assigned to a specific unit's Globally Unique Identifier (GUID), returning true(1) if assigned and false(2) if not. Writing false(2) is the mechanism for deleting a unit from the stack, purging all data the stack holds about that unit, so an admin uses this to formally remove a decommissioned or replaced unit. For example, when physically removing a failed stack member permanently, the admin sets its pdnUnitAssigned to false(2) to clear its configuration and stack data rather than leaving a stale entry.