This counter counts IGMP queries discarded because the ingress port was in a blocking state -- for example during Spanning Tree Protocol convergence or a storm-control block -- rather than administratively down. On this element, seeing this counter increase in bursts that line up with topology changes points to STP recalculation events temporarily suppressing multicast query processing on that port. For instance, a burst of a dozen discards exactly when a redundant uplink takes over after a primary link failure is consistent with the port sitting in an STP blocking or listening state during convergence.