A management information base (MIB) is used to store the structured information representing network elements and their attributes. The structure itself is defined in a standard called the structure of management information (SMI), which defines the data types that can be used to store an object, how those objects are named, and how they are encoded for transmission over a network.

MIBs are highly structured depositories for information about a device. Many standard MIBs exist, but more MIBs that are proprietary exist to uniquely manage different vendor’s devices. The original SMI MIB was categorized into eight different groups, totaling 114 managed objects. More groups were added to define MIB-II, which now replaces MIB-I.

All managed objects in the SNMP environment are arranged in a hierarchical or tree structure. The leaf objects of the tree, which are the elements that appear at the bottom of the diagram, are the actual managed objects. Each managed object represents some resource, activity or related information that is to be managed. A unique object identifier, which is a number in dot notation, identifies each managed object. Each object identifier is described using abstract syntax notation (ASN.1).

SNMP uses these object identifiers to identify the MIB variables to retrieve or modify. Objects that are in the public domain are described in MIBs introduced in Request for Comments (RFCs). They are readily accessible at: http://www.ietf.org

All vendors are encouraged to make their MIB definitions known. Once an assigned enterprise value has been given, the vendor is responsible for creating and maintaining sub-trees.