What is the MIB?

The MIB, or Management Information Base, is an ASCII text file that describes SNMP network elements as a list of data objects. Think of it as a dictionary of the SNMP language - every object referred to in an SNMP message must be listed in the MIB.

What does the MIB do?

The fundamental purpose of the MIB is to translate numerical strings into human-readable text. When an SNMP device sends a Trap or other message, it identifies each data object in the message with a number string called an object identifier, or OID. (OIDs are defined more fully later in this paper.)

The MIB provides a text label called for each OID. Your SNMP manager uses the MIB as a codebook for translating the OID numbers into a human-readable display.

Why do I need the MIB?

Your SNMP manager needs the MIB in order to process messages from your devices. Without the MIB, the message is just a meaningless string of numbers.

How do I get the MIB into my SNMP manager?

Your SNMP manager imports the MIB through a software function called compiling. Compiling converts the MIB from its raw ASCII format into a binary format the SNMP manager can use.

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 (Remote Telemetry Unit) 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 MIBs so you can have a realistic idea of what capabilities you have. When you're evaluating new SNMP equipment, examine its MIB file carefully before you purchase.

Prev Page: About the Author
Next Page: MIB White Paper: What Features Do I Need in an SNMP RTU?