Learning How to Create Behavior Models - How to Use Polls - How to Create a Poll -
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How to Create a Poll

In this scenario, you want to know which of the CriticalDevices nodes are experiencing high traffic. To accomplish this, you must create and enable a poll to check for this condition.

This scenario includes the following four activities:

1. Creating a New Poll
2. Writing a Poll Condition
3. Enabling a Poll
4. Modifying a Poll Condition

Creating a New Poll

This first activity will step you through the first stage of the process of creating a poll that checks for high traffic.

 
  To create a new poll:

1. Open the NerveCenter Client and connect to the appropriate NerveCenter Server.

2. From the Admin menu, choose Poll List.

   NerveCenter displays the Poll List window.

   Poll List Window

   

   Click the thumbnail above to view full-sized image.

   The Poll List window contains summary information about all poll definitions in the NerveCenter database for the active server. From this window you can open existing poll definitions or create new ones.

3. Select New.

   NerveCenter displays the Poll Definition window.

   Poll Definition Window

   

   Click the thumbnail above to view full-sized image.

4. In the Name field, type the name for your new poll definition, 1CheckTraffic.
5. From the Property list select myNodes.

   In the last chapter you assigned a particular set of nodes to the CriticalDevices property group. Since myNodes is unique to the CriticalDevices property group, when you select it you are telling NerveCenter to monitor only that particular set of nodes.

6. Leave Port blank.

   By leaving the Port text field blank you are telling this poll to communicate with each node on the port specified in the node's definition. (This would have been done by your network administrator.)

7. In the Poll Rate area, type 30 in the field and select the Seconds button.

   This sets the poll rate at 30 seconds.

You are now ready to define the core of your poll, the poll condition. The next activity will step you through that process.

Writing a Poll Condition

The core of each poll is its poll condition. A poll condition is a Perl script describing the conditions the poll should monitor. The poll condition also defines what trigger to fire when the poll detects those conditions.

This next activity will step you through the process of writing a poll condition for the 1CheckTraffic poll.

 
  To write a poll condition:

1. In the Poll Definition window, select the Poll Condition tab.

   NerveCenter displays the Poll Condition page.

   Poll Condition Page

   

   Click the thumbnail above to view full-sized image.

2. From the Base Object drop-down list, select ifEntry.

   Selecting this Management Information Base (MIB) base object tells the poll condition to reference only the ifEntry object.

3. In the Attribute list, double-click the attribute ifInOctets.

   ifEntry.ifInOctets appears in the Poll Condition text field.

   ---

   Note    Although you may include as many attributes as you like in a poll condition, each poll may use only one MIB base object.

   ---

4. In the Poll Condition text field, position the cursor before ifEntry.ifInOctets. Then type if( so that the expression states this:
      if( ifEntry.ifInOctets
5. With the cursor still at the position between if( and ifEntry.ifInOctets, right-click. Select Other functions, then delta.

   The word delta and a left parenthesis appears in the expression.

   The delta in this expression will return the difference between the values of ifEntry.ifInOctets taken over two consecutive polling instances.

6. Type in the necessary characters to complete the expression, so that it looks like the following:
      if( delta( ifEntry.ifInOctets) >= 5)
   {
   
   }

   To ensure that this poll will find a high-traffic condition, a low number for ifInOctets (five) is being used. In a real poll, you will want to define poll conditions based on the performance statistics for your network.

7. Position the cursor on the line between the two brackets and right-click. Select Other functions, then FireTrigger.

   The word FireTrigger and a left parenthesis appears in the expression.

8. Type "portTraffic");

   This tells the poll to fire the trigger portTraffic if it detects a difference between the values of ifEntry.ifInOctets of two successive polls to be at least five.

   The entire expression should looks like this:

   
      if(delta( ifEntry.ifInOctets)>=5)
   {
   FireTrigger( "portTraffic");
   }

   ---

   Tip    You can always type the entire expression manually. Right-click selections allow you to see what elements are available to build a poll condition. Just be sure to use the correct syntax.

   ---

9. Select Save.

You have now completed writing your poll condition. Before 1CheckTraffic can begin polling, you must complete a few more steps. The next section will explain those.

Enabling a Poll

You have just completed creating the 1CheckTraffic poll, which will poll all the nodes in the CriticalDevices property group for the number of ifEntry.ifInOctets. When the poll detects high-traffic conditions (what we've defined as a difference of five), it will fire the trigger portTraffic.

For this poll to begin actively polling, it must be enabled. This activity steps you through that process.

 
  To enable a poll:

1. In the Poll Definition window, select the Poll tab.

   NerveCenter displays the Poll page.

   Poll Page

   

   Click the thumbnail above to view full-sized image.

   Notice that the poll condition you just entered now appears in the poll condition window on the Poll page.

2. In the Enabled frame, select On.

   Notice that once the poll is enabled, all active fields and buttons are grayed out. A poll must be disabled to be modified.

3. Select Save.

You have just enabled the poll 1CheckTraffic. However, because of a NerveCenter feature called smart polling, this poll will not work until you create an alarm that is instantiated by its trigger. You will learn how to create this alarm in the next chapter, How to Use Alarms.

Modifying a Poll Condition

Before you create an alarm associated with the 1CheckTraffic poll, you should modify the poll condition to improve the poll. This will give you a chance to see an additional feature of the poll list.

 
  To modify a poll condition:

1. From the Admin menu, choose Poll List.

   NerveCenter displays the Poll List window.

   Poll List Window

   

   Click the thumbnail above to view full-sized image.

   Notice that the 1CheckTraffic poll is listed as being enabled. You will need to turn it off before we can modify it.

2. Right-click on the 1CheckTraffic poll.

   Notice that the pop-up menu gives you several ways to alter the poll without entering the Poll Definition window.

3. Select Off.

   You could also have turned off the poll from within the Poll Definition window.

4. Select Open.
5. In the Poll Definition window, select the Poll Condition tab.
6. Modify the poll expression in the Poll Condition field so that it looks like this:
      if((delta( ifEntry.ifInOctets )>=5) and
   (delta( ifEntry.ifOutOctets )>=5))
   {
   FireTrigger( "portTraffic" );
   }

   The modified poll will now check for an increase of incoming traffic, as well as outgoing.

7. In the Poll Definition window, select the Poll tab.

   The Poll Definition Window Showing the Modified Poll Condition

   

   Click the thumbnail above to view full-sized image.

8. In the Enabled frame, select On.
9. Select Save.

Now you have created, modified, and enabled the 1CheckTraffic poll. In the next chapter you will create an alarm that will transition states when your new poll generates the portTraffic trigger.