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Why is the MIB important?

Because as far as SNMP managers and agents are concerned, if a component of a network device isn't described in the MIB, it doesn't exist.

For example, let's say you have an SNMP RTU with a built-in temperature sensor. You think you'll get temperature alarms from this device - but you never do, no matter how hot it gets. Why not? You read the RTU's MIB file and find out that it only lists discrete points, and not the temperature sensor. Since the sensor isn't described in the MIB, the RTU can't send Traps with temperature data.

Why do I need to understand the MIB?

As you can see, the MIB is your best guide to the real capabilities of an SNMP device. Just looking at the physical components of a device won't tell you what kind of Traps you can get from it. You might think it's strange that a manufacturer would add a component to a device and not describe it in the MIB. But the fact is, a lot of devices have sketchy MIBs that don't fully support all their functions.

When you're planning your SNMP monitoring, you need to be able to read the MIB so you can have a realistic idea of what capabilities you have. And if you're evaluating new SNMP equipment, ask the vendor for the MIB and examine it carefully before you purchase.

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