The port's current state as defined by application of the Spanning Tree Protocol. This state controls what action a port takes on reception of a frame: discarding(1): Port receives configuration messages, but does not forward packets. learning(2): Port has transmitted configuration messages for an interval set by the Forward Delay parameter without receiving contradictory information. Port address table is cleared, and the port begins learning addresses. forwarding(3): Port forwards packets, and continues learning addresses. For ports which are disabled (see xstInstancePortEnable), this object will have a value of discarding(1).