Chapter 9. Polling and Thresholds
SNMP gives you the ability to poll your devices regularly, collecting their management information. Furthermore, you can tell the NMS that there are certain thresholds that, if crossed, require some sort of action. For example, you might want to be notified if the traffic at an interface jumps to an extremely high (or low) value; that event might signal a problem with the interface, or insufficient capacity, or even a hostile attack on your network. When such a condition occurs, the NMS can forward an alarm to an event-correlation engine or have an icon on an OpenView map flash. To make this more concrete, let’s say that the NMS is polling the status of an interface on a router. If the interface goes down, the NMS reports what has happened so the problem can be quickly resolved.
SNMP can perform either internal or external polling. Internal polling is typically used in conjunction with an application that runs as a daemon or a facility such as cron that periodically runs a local application. External polling is done by the NMS. The OpenView NMS provides a great implementation of external polling; it can graph and save your data for later retrieval or notify you if it looks like something has gone wrong. Many software packages make good NMSs, and if you’re clever about scripting you can throw together an NMS that’s fine-tuned to your needs. In this chapter, we will look at a few of the available packages.
Polling is like checking the oil ...