White Papers - NerveCenter 3.7: An Overview - How Behavior Models Work - Alarms -
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Alarms

Alarms are key to the operation of behavior models. An alarm is a finite state machine that defines the operational states it wants to detect and transitions from one state to the next when the proper trigger is received. Each transition is triggered by its own set of network data, which is defined in the NerveCenter object that generates the associated trigger. Transitions can also be driven by any alarm action that causes a trigger to be fired. If actions are associated with a transition, the server performs these actions each time the transition takes place.

The following illustration shows the state diagram for a NerveCenter alarm called IfUpDownStatus. IfUpDownStatus monitors the operational status of interfaces on managed nodes. If an interface is down, an inform action notifies the network management platform.

IfUpDownStatus Alarm

Each state is depicted as an icon in the diagram. The state icons are color coded to represent a particular level of severity.

The alarm contains four states related to the status of an interface:

• Up -- The interface is up. The current (operational) and desired (administrative) statuses are set to 1 (defined in RFC1213 as up). This state has a severity level of Normal.
• Administratively down -- Both the current (operational) and the desired (administrative) statuses are set to 2, defined in RFC1213 as down.
• Testing -- Either the current (operational) or desired (administrative) status is set to 3, defined in RFC1213 as test mode.
• Operationally down -- The current (operational) status is down but the desired (administrative) status is up. This state has a high severity level of Major. All transitions leading to this state include an alarm action that sends an inform to NerveCenter or to the platform.

The ifStatus poll fires all the triggers that transition the IfUpDownStatus alarm. The poll is designed to evaluate the MIB base object attributes ifAdminStatus and ifOperStatus, which belong to the ifEntry base object in the interfaces MIB-II group. The poll fires four triggers -- one for each of the four states previously described -- based on the values returned for the two attributes. The alarm correlates the data it receives from the poll and transitions based on the combinations shown in the following table.

Correlation of IfEntry Attributes in the IfUpDownStatus Alarm

In this alarm, a trigger representing a condition other than up for either attribute -- ifAdminStatus or ifOperStatus -- transitions the alarm from the Up state. A subsequent trigger representing a condition other than up for the remaining attribute then transitions the alarm to a different state. The state to which it transitions depends on the combination of the values for the two attributes.