This is the maximum period, in milliseconds, between IIH PDUs on multiaccess networks at this level for LANs; the value at L1 is used as the period between Hellos on L1L2 point-to-point circuits, and setting this value at level 2 on an L1L2 point-to-point circuit results in an InconsistentValue error. A subtlety worth knowing: on a point-to-point circuit running both levels, only the level-1 instance of this timer actually governs the shared Hello interval, so trying to configure the level-2 instance separately on such a circuit is explicitly rejected rather than silently ignored. For example, an admin trying to set a different Hello interval at level 2 on an L1L2 point-to-point serial link would have that SET rejected, since only the level-1 value actually controls Hello timing on that circuit.