Reports a port's current Spanning Tree Protocol state, such as discarding(3), learning(4), or forwarding(5), when the port itself is enabled; it reports no-stp-enabled(7) if the port is administratively disabled for STP, or err-disabled(8) if the switch has shut the port down due to an error condition. Admins check this to see exactly where in the STP convergence process a given port currently sits; a port stuck in discarding may indicate a blocked redundant link.