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Database used for managing the entities in a communication network

A management information base (MIB) is a database used for managing the entities in a communication network. Most often associated with the Simple Network Management Protocol (SNMP), the term is also used more generically in contexts such as in OSI/ISO Network management model. While intended to refer to the complete collection of management information available on an entity, it is often used to refer to a particular subset, more correctly referred to as MIB module. Objects in the MIB are defined using a subset of Abstract Syntax Notation One (ASN.1) called "Structure of Management Information Version 2 (SMIv2)" The software that performs the parsing is a MIB compiler. The database is hierarchical (tree structured) and each entry is addressed through an object identifier (OID). Internet documentation RFCs discuss MIBs, notably , "Structure and Identification of Management Information for TCP/IP based internets", and its two companions, , "Management Information Base for Network Management of TCP/IP based internets", and , "A Simple Network Management Protocol".

Abstract Syntax Notation One (ASN.1) is a standard and flexible notation that describes data structures for representing, encoding, transmitting, and decoding data. It provides a set of formal rules for describing the structure of objects that are independent of machine specific encoding techniques and is a precise, formal notation that removes ambiguities. ASN.1 is a joint ISO and ITU T standard, originally defined in 1984 as part of CCITT X.409:1984. ASN.1 moved to its own standard, X.208, in 1988 due to its broader applicability. The substantially revised 1995 version is covered by the X.680 standards series. An adapted subset of ASN.1, Structure of Management Information (SMI), is specified for use in SNMP to define sets of related MIB objects; these sets are termed MIB modules.

The first version of the Structure of Management Information (SMIv1) specifies the use of a number of SMI specific data types, which are divided into two categories: simple data types and application wide data types.

The SNMPv1 SMI defines highly structured tables that are used to group the instances of a tabular object (that is, an object that contains multiple variables). Tables are composed of zero or more rows, which are indexed in a way that allows an SNMP manager to retrieve or alter an entire row with a single Get, GetNext, or Set command.

The second version of the SMI (SMIv2) is described in and It enhances and adds to the SMIv1 specific data types, such as including bit strings, network addresses, and counters. Bit strings are defined only in SMIv2 and comprise zero or more named bits that specify a value. Network addresses represent an address from a particular protocol family. Counters are non negative integers that increase until they reach a maximum value and then return to zero. In SMIv1, a 32 bit counter size is specified. In SMIv2, 32 bit and 64 bit counters are defined. SMIv2 also specifies information modules, which specify a group of related definitions. Three types of SMI information modules exist: MIB modules, compliance statements, and capability statements. MIB modules contain definitions of interrelated managed objects. Compliance statements provide a systematic way to describe a group of managed objects that must be implemented for conformance to a standard. Capability statements are used to indicate the precise level of support that an agent claims with respect to a MIB group. An NMS can adjust its behavior toward agents according to the capabilities statements associated with each agent.

MIB modules are occasionally updated to add new functionality, remove ambiguities and fix defects. These changes are made in conformance to section 10 of and section 5 of An example of a MIB module that has been updated many times is the important set of objects that was originally defined in , also known as "MIB II". This MIB module has since been split up and can be found in MIB modules such as "Management Information Base for the Internet Protocol (IP)", "Management Information Base for the Transmission Control Protocol (TCP)", "Management Information Base for the User Datagram Protocol (UDP)", "The Interfaces Group MIB" and "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)".

There are a large number of MIBs defined by standards organizations like the IETF, private enterprises and other entities.