This is the receive-side counterpart: it counts LTMs other devices have sent that arrived at this device, whether this device is the ultimate target or an intermediate hop the trace passes through. Because linktrace is deliberately triggered, this counter rising is direct evidence some remote operator is actively path-tracing through or to this device right now, useful context if an admin is simultaneously fielding a connectivity complaint from that same direction. A cluster of increments here at the same time a neighboring domain's NOC opens a ticket about reachability to this segment strongly hints they are linktracing toward this device as part of their own diagnosis.