How to build a Threshold Shooter that only monitors those rows of a table that match a certain pattern?

Definition of the problem

Imagine that you are responsible for a large redundant network with hundreds of switches and/or routers and that on a certain day one of the Gbic interface modules in one of your backbone switches gets down and stops working. Big chance that you wouldn't notice! The redundancy in your network would easily take care of redirecting the traffic that would normally traverse the interface mentioned above to another link.

Needless to say that this needs some attention. The solution would be to monitor the interface status of all Gigabit fiber interfaces of the backbone routers and generate an alert when one would go down.

The screen-shot below shows the interfaces table of the switch. As you can see only the upper 8 interfaces are Gigabit interfaces, all other ports are 100Mb (FastEthernet).

As you of course already know, the status of an interface can be monitored by checking the the value of the ifOperStatus field (value = 1) of the interface through a Threshold Shooter. In this case the Threshold Shooter would only need to monitor the 8 Gigabit ports. But how would such a Shooter be build?

The answer is by using the Index filter option! The steps below describe how to use this option.

Step 1. Building a basic Threshold Shooter that monitors the status of all interfaces of the switch.

For building the basic Threshold Shooter we'll use the Shooter wizard!

1. Switch to Designer mode
2. Right-click the backbone switch and select Define Shooters (Wizard).
3. Click Next (The wizard start inspecting the switch
4. When Inspecting has finished click Next.
5. Choose B. Interfaces from the selection box and click Next.
6. Choose R. Detect if the status of an interface has changed from up to down and click Next.
7. Choose F. Threshold Shooter and click Next.
8. Choose B. 10 seconds and click Next.
9. Choose C. All instances and click Next.
10. Enter a name for the new Shooter (i.e. Gigabit_Link_Status) and click Next.
11. Verify all settings and if ok click Build.
12. Choose A. Do not start the Shooter and click Finish.

The configuration of the basic Threshold Shooter that we just built shows:

When this Shooter is started (right-click the switch on the map and select Shooters?Properties, choose Background Shooters, right-click the Shooter in the Available box and select Start this Shooter...) the Threshold control window shows:

All interfaces of the switch are monitored. Not only the GigabitEthernet interfaces.

Step 2. Adding an instance filter so that only the GigabitEthernet interfaces are monitored.

1. Right-click the switch again and select Define Shooters (Manually).
2. Click to select the Gigabit_Link_Status Shooter in the Shooters box.
3. Right-click the ifOperStatus Shooter target and select Search for this node in the MIB tree (This will open the ifEntry branch in the MIB tree where the ifOperStatus field is).
4. Right-click on the ifEntry node (the parent of the ifOperStatus field) and select Inspect.
5. Right-click the ifDescr field and select Add as an Instance Filter to ...
6. The Instance Filter configuration dialog box opens.
7. Select Begin with from the selection box, select the String radiobutton and enter the string "GigabitEthernet" into the Value box.
   
8. Click Save. The Shooter configuration now shows.
   
9. Close the Define Shooters window.

The Threshold control window now shows: