This value turns on or off Restricted Group Registration (per IEEE 802.1t) on a given bridge port; when true(1), a new dynamic GMRP multicast group entry can only be created if a matching static filtering entry already exists for that group with Normal Registration control, per the source description. A network administrator enables this on ports where they want tight control over which multicast groups can be dynamically learned, preventing unauthorized or unexpected multicast group registrations. For example, setting this to true(1) on an edge port would block GMRP from dynamically registering a multicast group there unless it's already explicitly permitted by a static entry.