SNMP Information and OID Identification

SNMP (Simple Network Management Protocol) is an application-layer protocol used to manage and monitor network devices and their functions. It is one of the most commonly used network monitoring tools and supported by a wide range of manufacturers across multiple device types.

As part of this coverage we will focus on two of the main components of SNMP.

Management Information Base (MIB) a collection of information organized hierarchically in a “tree” structure written in a human-readable format. Each entry in the MIB file related to a piece of information and assigned a number. A device can use multiple MIB files. These can be generic or vendor specific.

Object Identifier (OID) a numeric string used to uniquely identify an object. This number is based on the information contained in the MIB file. The OID can contain an index value when it is part of a table. OIDs return a value from the device. The associated MIV declares the syntax of this value. Depending on the information for the OID in the MIB it may also contain pass or fail state information.

MIBs may be thought of as phone books and the OIDs telephone numbers. If you do not have the MIB references, you do not know what the OID is calling. Another way to view this is a directory structure. Folders, sub-folders (MIBs) and files (OIDs).

Although a MIB file contains information for its monitoring components. It does not return details for other MIBs that may be in use on the device. To see all OID information returned from the device it is useful to use a MIB browser or SNMP Walk tool. For example, iReasoning’s MIB Browser.

These tools allow you to walk through all the OIDs on the device regardless of the MIB they are associated with. Viewing live information from that device. The returned OIDs, their index number, current value etc.

The following sections covers…