This read-only Counter64 counts queries discarded because the ingress port was down at the moment the query arrived. A nonzero count right after a known link flap is expected and benign, but a steady trickle on a port that monitoring shows as up points to a state-tracking mismatch worth investigating; because it is drawn from this table's currently-accumulating, short-interval bin, it reflects only the last few minutes of activity, so it's the value to watch for a fast-forming problem rather than a long-term trend. On an uplink toward the multicast-enabled core router, a count of 1,186 over the last 15 minutes is the kind of number an admin would trend against the join/leave rate on the same port to judge whether it's normal channel-surfing or an anomaly worth a closer look.