In Checkmk 2.0.0p1 you can set a rule for multicast packet rates in Network interfaces and switch ports and ‘make the check go warning or critical whenever the percentual packet rate or the absolute packet rate of the monitored interface reaches the given bounds’.
But is it possible to set a packet rate that makes the check set an alarm if the rate goes below that level, that is, a low level alarm?
No, this is not possible. Only upper thresholds are configurable.