Designing and Managing Behavior Models
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Behavior Models and Their Components - NerveCenter Objects - Polls -
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Polls
A NerveCenter poll periodically sends an SNMP message to a set of nodes, requesting information from the agents running on those nodes. When the poll receives this information from a node, it uses the information in the evaluation of a poll condition, which may cause a trigger to be fired. For example, a poll may fire a trigger if the number of discarded packets on an interface is too high. The poll condition must be able to fire at least one trigger, and may be capable of firing several. These triggers can cause alarms to be instantiated, to change states, or perform actions -- under the right circumstances.
The key attributes of a poll are shown in the following figure.
Poll's Data Set
Note The names of the data members shown above match the labels used in NerveCenter's Poll Definition window, where you create and modify poll objects.
The table below explains what information these data members contain and, where appropriate, how NerveCenter uses that information.
Definitions of Poll Attributes
|
Data Member
|
Definition
|
|---|
Name |
A unique name that you assign to the poll. |
Property |
The Property attribute is a string. This string determines (in part) whether a poll will request MIB data from a particular node. Only if the node's property group contains the poll's property can polling possibly occur. However, before a poll will request information from a node's SNMP agent, other conditions must be satisfied as well. For further information, see the explanation below for Poll Condition. |
Port |
Optional. If you specify a port number here, NerveCenter will send the poll to this port on the nodes that are configured to receive the poll. Otherwise, NerveCenter will send the poll to the port specified in each node's definition. |
Poll Rate |
The number of seconds, minutes, or hours between polls. |
Enabled |
A poll's enabled status (Off or On) is similar to a node's Managed status. That is, if a poll is disabled, it will never send a request to an SNMP agent. |
Poll Condition |
The Poll Condition is a Perl script that can fire one or more triggers. Which trigger is fired (if any) depends of what data the poll retrieves from an SNMP agent. Generally, this data is used in evaluating an if statement.
This poll condition must be expressed in terms of one MIB base object. For example, a valid condition would be:
if (delta( snmp.snmpInBadCommunityNames ) >= 1 or
delta( snmp.snmpInBadCommunityUses ) >= 1) {
FireTrigger("AuthFail");
}
In this case, the base object is snmp. The name of this base object must be one of the properties in a node's property group before the node can receive a request from a poll with this poll condition. |
Suppressible |
A poll's Suppressible attribute works in conjunction with a node's Suppressed attribute. If a node is suppressed and a related poll is suppressible, that poll will not query that node. If a poll is not suppressible, then it will poll even a suppressed node. Generally, the only polls that are insuppressible are those designed to determine when an unresponsive node becomes responsive again. When a node becomes responsive, the behavior model of which the poll is a part can change the status of the node from suppressed to unsuppressed. (You set an attribute of a node using the Set Attribute alarm action.) |
If a poll fires a trigger, that trigger has the following attributes.
Trigger's Data Set
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The table below explains what information these data members contain.
Definitions of Trigger Attributes
|
Data Member
|
Definition
|
|---|
Name |
The name of the trigger, which is defined in the poll definition. |
Node name/IP address |
The name or IP address of the node that responded to the poll and caused the trigger to be fired. |
Subobject |
In general, the Subobject has a value of the form BaseObject.Instance. BaseObject is the name of the MIB base object that the poll inquired about, and Instance is the unique identifier associated with a row of MIB data returned by the poll. In most cases, Instance is the number associated with a particular interface on the node. The subobject, however, can also be an arbitrary string. The important thing is that subobjects can be used to uniquely identify alarm instances so that triggers can be directed to exactly the right alarm instance. |
Property |
The Property, as always, is simply a string. A trigger fired by a poll does not have a property, but as you'll see later, other triggers do. |
Variable bindings |
The trigger also contains the values of the MIB attributes referred to in the Poll Condition. Each attribute and its value are called a variable binding. |
A trigger's Name, Node name/IP address, Subobject, and Property are all important when it comes to determining what effect, if any, a trigger has on an alarm. You'll find more on this subject in the section Constructing Behavior Models.