FAQ: The SNMP MIB - Definition, Versions, How To Read MIBs
- How to Read and Understand the MIB (downloadable PDF)
- Why is the MIB important?
- Tactics for resolving common MIB problems
What are MIBs?
A MIB is a formatted text file that lists all of the data objects used by a particular piece of equipment.
How the MIB works in 3 steps:
- The manufacturer of your device will supply you with a MIB file.
- You'll load the MIB into your SNMP manager.
- Your SNMP manager will use the MIB to interpret the incoming messages from your new device.
When you buy a device that uses SNMP (for example, a managed switch), you'll tell it to send messages to your central SNMP manager. But there are tens of thousands of different SNMP devices, and your manager doesn't natively understand each one.
That's where the MIB comes in. The manufacturer of your device will supply you with a MIB file (usually a download from their website) that you'll load ("compile") into your SNMP manager (If you've ever installed a device driver on a PC, you understand this concept). Without the MIB for message translation, communication simply won't happen.
The manager uses MIB files from each agent to decode the OIDs (strings of numbers) and translate them into meaningful information.
What is an "SNMP-Compliant" MIB?
A MIB contains definitions and info about the properties of managed resources and the services that the agents (devices) support. The features of resources, as defined in an MIB, are called "managed objects" or "management variables".
A management station gets and sets objects in the MIB, and an agent notifies the management station of events using messges called (somewhat oddly) "traps". All message exchanges between the management station and its agents take place using SNMP. The MIB at the management station contains network management info taken from the MIBs of all the managed parts in the network.
Why do I need the MIB?
Your SNMP manager needs the MIB in order to process messages from your devices. The MIB is also your best guide to the real capabilities of an SNMP device. You need to be able to read the MIB so that you can have a good idea of what assets you do have.
How do I look at a MIB?
One of the best tactics for addressing MIB problems is to simply read through the file. As a MIB (SNMP) file is just ASCII text, you can view it in any word processor or text editor (even Notepad). Some manufacturers provide grouped MIBs in binary format, but those aren't readable. You want the raw ASCII version of the MIB (SNMP) file.
What is SNMP?
The Simple Network Management Protocol, or SNMP, is the standard protocol for the Internet. The Internet Engineering Task Force (IETF) developed it.
SNMP is used to manage network devices that span firewalls or embedded devices.
SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be sorted (and sometimes set) by managing applications.
What versions of SNMP are available?
There are several SNMP versions, including v1, v2, and v3.
The SNMP v1 network management architecture contains:
- Network Management Station (NMS) - Workstation that hosts the network management app.
- SNMPv1 network management application - Polls management agents for information and provides control info to agents.
- SNMPv1 management agent(s) - Provides info contained in the MIB to management applications and may accept control information.
SNMP v2 specs include the following new capabilities:
- Manager to manager communication to support multiple / distributed managers and mid-level managers.
- Better security (known as "Secure SNMP") by specifying three layers of security.
- Improved efficiency and performance through the addition of bulk transfers of data.
SNMP v3 specs include the encryption required by security-conscious organizations. With an SNMPv3 mediator, it's possible to upgrade older equipment to SNMPv3.