Structure of Management Information
How management information is represented and what kind of data it can contain is defined by The Structure of Management Information Version 1 (SMIv1 , RFC 1155) and The Structure of Management Information Version 2 (SMIv2 , RFC 2578). Managed systems expose their configuration in the form of managed objects or variables. The values of managed objects can then be queried and sometimes set by managing applications.
Managed objects are describe by several attributes. The most important are object identifier (name), type, and encoding.
Object Identifiers
Object Identifier (OID) uniquely defines a managed object.
Managed objects are organized into a treelike hierarchy. Object ID represents the place of a particular object in this hierarchy as a series of integers based on the nodes in the tree, separated by dots (.). This is known as a numeric form of OID. There's also a human-readable form, that represents each OID as a series of names.
 | Example: A textual description of a managed entity is represented by an object with numeric ID |
Type
A type of managed object within context of SNMP is defined by a subset of Abstract Syntax Notation One (ASN.1). ASN.1 specifies a machine-independent form of data representation and transmission between managers and agents.
There are several basic types defined. They can be used to define more complex objects, containing other objects and so on, thereby composing parts of treelike hierarchy we mentioned a bit earlier.
The descriptions of managed object are typically grouped together according to a specific management task, device, or vendor. These descriptions are stored in MIB files. They are used by network management system to monitor and manage network devices, services, tasks, etc. For example, Iotellect Network Manager is provided with a set of the most important MIBs out of box. Vendor- or task-specific MIBs can be added to extend functionality of Iotellect Network Manager. See the Managing SNMP Files sections for more details about MIB files management in Iotellect Network Manager.
In SNMP a set of related variables can be grouped together to form larger structures represented as tables. Thus, objects can contain values of two kinds: scalars or tables. Scalars have a single value. For example, the iso.org.dod.internet.mgmt.mib-2.interfaces.ifNumber (1.3.6.1.2.1.2.1) has a scalar number that represents the total number of interfaces (ports) available on a network device. Tables provide several records with the identical structure. For example, iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable (1.3.6.1.2.1.2.2) variable contain a list of interface entries, each representing details about a particular network interface, like its display string, physical address, bandwidth etc.
Encoding
Managed objects are encoded into string of octets to be transmitted over network. The encoding and decoding algorithms used in SNMP are described by Basic Encoding Rules (BER).
Was this page helpful?