This object contains an appropriate value to be used for mplsLabelStackIndex when creating entries in the mplsLabelStackTable. The value 0 indicates that no unassigned entries are available. To obtain an mplsLabelStackIndex value for a new entry, the manager issues a management protocol retrieval operation to obtain the current value of this object. After each retrieval operation, the agent should modify the value to reflect the next unassigned index. After a manager retrieves a value the agent will determine through its local policy when this index value will be made available for reuse.