Facility Alarms for children objects is not raised for failure of a parent object. For example, when port fails (or is shut down) there is not a set of port alarms raised.
When a parent alarm is cleared, children alarms that are still in occurrence on the node appears in the active alarms list. For example, when a port fails there is a port alarm, but if the port is later shut down the port alarm is cleared (and a card alarm will be active). If the card comes back into service, and the port is still down, then a port alarm becomes active once again.
The supported Facility Alarm hierarchy is as follows (parent objects that are down cause alarms in all children to be masked):
CPM -> Compact Flash
IOM/IMM -> MDA -> Port -> Channel
A masked alarm is not the same as a cleared alarm. The cleared alarm queue does not display entries for previously raised alarms that are currently masked. If the masking event goes away, then the previously raised alarms will once again be visible in the active alarm queue.