This read-only INTEGER, though its source description is empty, reports this port's live 802.1D spanning tree state as one of spanning-tree-disabled, listening, learning, forwarding, or blocking. An administrator checks it to see whether the port is actually passing user traffic or being held back by spanning tree. For example, the admin sees a port stuck in spanning-tree-listening far longer than stActDelay would suggest, indicating a spanning tree convergence problem on that port.