This attribute specifies whether or not spanning tree protocol state for
this bridge port is controlled by the spanning tree protocol. In essence it
indicates the participation of this bridge port in the spanning tree
protocol, by accepting and acting on received bridge protocol data units
and by sending out the same.
on signifies that this bridge port's spanning tree port state is controlled
by the spanning tree protocol.
A value of off signifies that the spanning tree port state of this bridge
port is unaffected by the spanning tree protocol. This in effect puts the
bridge port out of reach of the spanning tree protocol and in the
forwarding state. Care should be taken while assigning a value of off to
this attribute, as this might cause network loops. Please do not set this
attribute to off unless you are absolutely sure about the effect of such an
action on your network topology.