This read-only Counter64 counts messages the router-side logic discarded because a join arrived on a port that is configured as a router port. This specifically flags a join coming in from the "wrong side" of the network — where the multicast router itself should be — which is usually a topology or port-role misconfiguration rather than a subscriber issue; because it is drawn from the most recently completed 24-hour bin, frozen once the day rolled over, it is frozen and safe to use for day-over-day comparison, since no further traffic will ever be added to it. On a residential VLAN used for multicast video delivery, a count of 2,405 over the last completed collection window 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.