A management information base (MIB) is a formal description of a set of network objects that can be managed using the Simple Network Management Protocol (SNMP). The format of the MIB is defined as part of the SNMP. (All other MIBs are extensions of this basic management information base.) MIB-I refers to the initial MIB definition; MIB-II refers to the current definition. SNMPv2 includes MIB-II and adds some new objects.
There are MIBs (or more accurately, MIB extensions) for each set of related network entities that can be managed. For example, there are MIB definitions specified in the form of Requests for Comments (RFCs) for AppleTalk, domain name system (DNS), Fiber Distributed-Data Interface, and RS-232C network objects. Product developers can create and register new MIB extensions. Companies that have created MIB extensions for their sets of products include Cisco, Fore, IBM, Novell, QMS, and Onramp.