A Boolean value set by management. If TRUE causes the Port not
to be selected as Root Port for the CIST or any MSTI, even it has
the best spanning tree priority vector. Such a Port will be selected
as an Alternate Port after the Root Port has been selected. This
parameter should be FALSE by default. If set it can cause lack of
spanning tree connectivity. It is set by a network administrator to
prevent bridges external to a core region of the network influencing
the spanning tree active topology, possibly because those bridges are
not under the full control of the administrator.
This administrator configuration is also known as 'Root Guard'.