This read-only 64-bit counter tallies Layer 2 control protocol frames, such as STP or LACP, discarded in the access-to-network direction during the interval, per the description. Admins monitor this to confirm Layer 2 control-protocol tunneling/filtering policy is working as intended and to catch unexpected discards that could disrupt customer-side protocol operation. For example, if a customer's spanning-tree BPDUs are unexpectedly being blocked, a nonzero and rising value here would confirm the port is discarding those L2 control frames.