RCA stitcher sequence

The stitchers that are called by the RCA plug-in and the sequence in which stitchers are run to determine root cause.

1. When the Event Gateway passes an event to the RCA plug-in, the ProcessEvent.stch stitcher is called to handle the event. This event is called the trigger event.
2. The ProcessEvent.stch stitcher determines which stitcher to call, depending on the event state of the trigger event, as described in the following table:

   Event state of the trigger event	Stitcher that is called
   Occurred ReAwakened, ReOccurred Resync Updated	ProcessProblemEvent.stch
   Cleared Deleted	The ProcessResolutionEvent.stch stitcher processed cleared and deleted events. The TimedClearEventProcessing.stch stitcher reprocesses events that were suppressed by cleared or deleted events. This stitcher incorporates a delay of 30 seconds to prevent issues caused by events arriving close to each other.

3. Two triggers are called by the ProcessProblemEvent.stch stitcher to attempt to suppress the trigger event. These triggers are as follows:
   • The SuppressTrigger.stch stitcher determines whether the trigger event can be suppressed by an existing event.
   • For OSPF or BGP events, the PeerEntitySuppression.stch stitcher determines whether the trigger event can be suppressed by another event on the peer entity.
   If the SuppressTrigger.stch or the PeerEntitySuppression.stch stitchers cannot suppress the trigger event, the trigger event becomes root cause.
4. The RCA plug-in checks whether the trigger event is suppressed by another event on the same entity. That is, the check assesses if the trigger event is not the master event for the entity. If the trigger event is not the master event, it is prevented from suppressing other events, because the master event for the entity performs event suppression. In the subsequent steps, the ProcessProblemEvent.stch calls other stitchers, which attempt to use the trigger event to suppress other events. Each of the stitchers is run in turn.
5. The EntitySuppression.stch stitcher uses the trigger event to suppress other events on the exact same entity. The event that has the highest precedence on the entity suppresses all the other events on that entity.
6. The ContainedEntitySuppression.stch stitcher uses the trigger event to attempt to suppress other events by using contained entity principles. The event on the containing entity suppresses events on all contained entities.
7. The IsolatedEntitySuppression.stch stitcher uses the trigger event to attempt to suppress other events by using downstream entity principles.
8. The ConnectedEntitySuppression.stch stitcher uses the trigger event to attempt to suppress other events using by connected entity principles. For example, when two interfaces are connected and there is an event on both, the event on one of the interfaces suppresses the event on the other interface.