The Simple Network Management Protocol (SNMP) forms part of the internet protocol suite as defined by the Internet Engineering Task Force (IETF). SNMP is one of the key forms of technology that enabled the Internet's phenomenal growth.

SNMP is used in network management systems to monitor network-attached devices for conditions that require administrative attention. It consists of a set of standards for network management, which includes an Application Layer protocol, a database schema, and a set of data objects. SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried (and sometimes set) by managing applications.

Basic concepts of SNMP
In typical SNMP usage, there are a number of systems to be managed, and one or more systems managing them. A software component called an agent runs on each managed system and reports information via SNMP to the managing systems.Essentially, SNMP agents expose management data on the managed systems as variables (such as "free memory", "system name", "number of running processes", "default route"). The managing system can retrieve the information through the GET protocol operations or the agent will send data without being asked using TRAP or INFORM protocol operations.

In addition, management systems can also send configuration updates or controlling requests through the SET protocol operation to actively manage a system. Configuration and control operations are used only when changes are needed to the network infrastructure. Such monitoring operations are usually performed on a regular basis.The variables accessible via SNMP are organized in hierarchies. These hierarchies, and other metadata (such as type and description of the variable), are described by Management Information Bases (MIBs).

SNMP device information

Components of SNMP
The SNMP framework consists of master agents, subagents and management stations.

Master agent
A master agent is a piece of software running on an SNMP-capable network component, for example a router, that responds to SNMP requests from the management station. Thus, it acts as a server in client-server architecture terminology. A master agent relies on subagents to provide information about the management of specific functionality. Master agents can also be referred to as managed objects.

Subagent
A subagent is a piece of software running on an SNMP-capable network component that implements the information and management functionality defined by a specific MIB. Some capabilities of the subagent are:

• Gathering information from managed objects
• Configuring parameters of the managed objects
• Responding to managers' requests
• Generating alarms or traps

Management station

The manager or management station is the final component in the MIB SNMP architecture. It functions as the equivalent of a client in the client-server architecture. It issues requests for management operations on behalf of a administrator or application and receives traps from agents as well.

SNMP terms & definitions

What is the MIB?
The MIB, or Management Information Base, is an ASCII text file that describes SNMP network elements as a list of data objects. It is essentially a dictionary of the SNMP language, where every object referred to in an SNMP message must be listed in the MIB.

MIBs describe the structure of the management data of a device subsystem by using a hierarchical namespace containing object identifiers (OID). Essentially, each OID identifies a variable that can be read or set via SNMP.

Role of the MIB
The primary purpose of the MIB is to translate numerical strings into readable text for humans. When an SNMP device sends a Trap or other message, it identifies each data object in the message with a number string called an object identifier, or OID. The MIB provides a text label called for each OID. Your SNMP manager uses the MIB as a codebook for translating the OID numbers into a human-readable display.

How the MIB is structured
The following keywords are used to define a MIB object:

Syntax
Defines the abstract data structure corresponding to the object type.

Access
Defines whether the object value may only be retrieved but not modified (read-only) or whether it may also be modified (read-write).

Description
Contains a textual definition of the object type. The definition provides all semantic definitions necessary for interpretation; it typically contains information of the sort that would be communicated in any commentary annotations associated with the object.

Costs and Limitations related to MIB SNMP

• The attractiveness of SNMP is its simplicity and relative ease of implementation. With this comes a price: e.g., the more fine grained information that is need or required, the less likely it is that it will be available.
• SNMPv1 uses the underlying User Datagram Protocol (UDP) for data delivery, which does not ensure reliability of data transfer.
• SNMP is best suited for network monitoring and capacity planning. SNMP does not provide even the basic troubleshooting information that can be obtained from simple network troubleshooting tools.
• SNMP agents do not analyze information; they just collect information and provide it to the network management application.
• SNMPv1 has minimal security capability. Because SNMPv1 lacks the control of unauthorized access to critical network devices and systems, it may be necessary to restrict the use of SNMP management to non-critical networks.
• SNMP out-of-the-box cannot be used to track information contained in application/user level protocols (e.g., radar track message, http, mail).

There are also concerns about the use of MIB SNMP practices in the real-time domain where bounded response, deadlines, and priorities are required.

Related Topics:
SNMP Trap
SNMP Trap Basics
Using SNMP Traps in a Network Management System
SNMP MIB
SNMP OID

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