SNMP (Simple Network Management Protocol is the protocol of network management)

SNMP (Simple Network Management Protocol is the simple network management protocol) is the widespread protocol which tasks include control of network devices and obtaining information on their work, in particular. As a rule, all modern managed network devices (workstations, notebooks, switches, printers, routers, modems, webcams, etc.) have a so-called Management information base (MIB — Management Information Base). This base contains the mass of useful information about a device status: performance counters, active processes, values of network traffic on interfaces, etc. In some devices the number of various records in such bases reaches tens of thousands. Each record in base is followed by a unique identifier of OID (object identifier). Knowing OID records in which the interesting parameter is stored, it is possible to configure the program on its control. The program for the SNMP protocol will be connected to the device, on OID to receive a parameter value and to compare it to a preset value. In case of mismatch of parameter to a preset value, the program signals about it. 

Usually when using SNMP there are managed and managing systems. The component called by the agent who sends reports to a managing system is a part of the managed system. On the substance of SNMP agents report management information to the managing systems as variables (such as "free memory", "system name", "the number of the working processes").

A managing system can obtain information through transactions of the GET, GETNEXT and GETBULK protocol. The agent can independently send data without request, using transaction of the TRAP or INFORM protocol. The managing systems can also send configuration updates or the controlling requests, using the transaction SET for direct manipulation by a system. Transactions of configuring and management are used only when changes in network infrastructure are necessary. Transactions of monitoring are usually executed on a regular basis.

Variable, available through SNMP, are organized in hierarchy. These hierarchies and other metadata (such as type and description of a variable) are described by Management information bases. Management Information Bases (MIBs)

SNMP does not define what information (what variables) the managed system should provide. On the contrary, SNMP uses the expanded model in which available information is defined by Management information bases (MIB — Management Information Base). Management information bases describe structure of control data of devices. They use the hierarchical namespace containing a unique identifier of an object (engl. object identifier (OID)). Roughly speaking, each unique identifier of an object identifies a variable which can be read or set through SNMP. MIBY use the notation defined in ASN.1.

The hierarchy of MIB can be represented as a tree with an anonymous root which levels are appropriated by the different organizations. At the highest level MIB OIDY belong to the different organizations which are engaged in standardization while at lower level of OIDY are selected with associated organizations. This model provides management on all layers of a network model of OSI as MIBY can be defined for any data types and transactions.

The managed object is one of any number of the characteristics specific to the managed device. The managed object includes one or more copies of an object (identified on OID) which actually variable.

There are two types of managed objects:

• Scalar objects define the single copy of an object.
• Tabular objects define multiple, connected copies of objects which are grouped in the tables MIB.

atInput which is the scalar object containing the single copy of an object, an integer number which shows a total quantity of the incoming packets AppleTalk on the network interface of the router can be an example of a managed object.

Object ID (OID) it is unique identifies a managed object in hierarchy of MIB.

The original is taken from the website of EQUICOM company