Indicates the port role on a particular Spanning Tree
instance for the RSTP protocol.
disabled -- this port has no role in this Spanning
Tree instance.
root -- this port has the role of root port in this
Spanning Tree instance.
designated -- this port has the role of designated
port in this Spanning Tree instance.
alternate -- this port has the role of alternate port
in this Spanning Tree instance.
backUp -- this port has the role of backup port in this
Spanning Tree instance.
boundary -- this port has the role of boundary port in
this Spanning Tree instance.
master -- this port has the role of master port in
this Spanning Tree instance.
This object could have a value of 'boundary' or 'master'
only when the object value of stpxSpanningTreeType is mst(4).