Chapter 6. SNMP Operation
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Version 1.2 Apr 2006
6.3 The Management Information Base
The management information base (MIB) includes a collection of managed objects. Managed
objects are defined as parameters that can be managed, such as specific information on device
configuring or on performance statistics values.
The MIB includes the definitions of relevant managed objects (MIB variables) for the specific
node. Various MIB's can be defined for various management purposes, types of equipment, etc. The
management data itself is a collection of integer, string and MIB address variables that contain all
the information necessary to manage the node.
A leaf object's definition includes the range of instances (values) and the "access" rights:
Read-only
Instances of an object can be read, but cannot be set.
Read-write
Instances of an object can be read or set.
Write-only
Instances of an object can be set, but cannot be read.
Not accessible
Instances of an object cannot be read, nor set.
6.4 MIB Structure
The MIB has an inverted tree-like structure (root over leaves), with each definition of a
managed instance forming one leaf, located at the end of a branch of that tree. Each "leaf" in the
MIB is reached by a unique path, therefore by numbering the branching points, starting with the
top, each leaf can be uniquely defined by a sequence of numbers. The formal description of the
managed objects and the MIB structure is provided in a special standardized format, called Abstract
Syntax Notation 1, or ASN.1 (pronounced A-S-N dot one).
Since the general collection of MIB's can also be organized in a similar structure, under the
supervision of the Internet Activities Board (IAB), any parameter included in a MIB that is
recognized by the IAB is uniquely defined.
To provide the flexibility necessary in a global structure, MIB's are classified in various
classes (branches), one of them being the experimental branch, another being the management
(mgmt) branch, and yet another the group of private (enterprise-specific) branch. Under the private
enterprise-specific branch of MIB's, each enterprise (manufacturer) can be assigned a number,
which is its enterprise number. The assigned number designates the top of an enterprise-specific
sub-tree of non-standard MIB's.
