This read-write field is the group-address counterpart to lportSmdsIaScrnOp, setting whether group-address screening, per lportSmdsGaScrnMap, operates as allow or disallow for multicast SMDS traffic on this interface. An admin configures this separately from individual-address screening because group, or multicast, SMDS traffic often has different access-control needs than point-to-point individual-address traffic. For example, a port might disallow only a couple of specific group addresses while its individual-address screening runs in strict allow mode, reflecting different trust levels for broadcast versus unicast SMDS traffic.