Description: The number of packets which this router has received from these sources and addressed to this multicast group address, which were dropped because they were received on an unexpected interface.

For RPF checking protocols (such as PIM-SM), these packets arrived on interfaces other than alaIpMcastRouteInIfIndex, and were dropped because of this failed RPF check. (RPF paths are 'Reverse Path Forwarding' path; the unicast routes to the expected origin of multicast data flows).

Other protocols may drop packets on an incoming interface check for different reasons (for example, BIDIR-PIM performs a DF check on receipt of packets). All packets dropped as a result of an incoming interface check are counted here.

If this counter increases rapidly, this indicates a problem. A significant quantity of multicast data is arriving at this router on unexpected interfaces, and is not being forwarded. For guidance, if the rate of increase of this counter exceeds 1% of the rate of increase of alaIpMcastRoutePkts, then there are multicast routing problems that require investigation.

Discontinuities in this monotonically increasing value occur at re-initialization of the management system. Discontinuities can also occur as a result of routes being removed and replaced, which can be detected by observing the value of alaIpMcastRouteTimeStamp.