This read-create RowStatus object governs the BUS entry, and the description states it cannot be set to active until the busIfIndex object has an appropriate value, with some implementations refusing row creation here entirely in favor of the LES MIB. This enforces that a BUS entry always has a real physical interface bound to it before it can come up, and on implementations without separate LES/BUS entities, this row creation may simply be refused in favor of managing the BUS through the LES MIB instead. An admin attempting to activate a BUS row before setting busIfIndex would get rejected by the agent, since the row lacks the mandatory interface binding needed to become operational.