Simple Network Management Protocol (SNMP) forms part of the internet protocol suite as defined by the Internet Engineering Task Force (IETF). SNMP is used in network management systems to monitor network-attached devices for conditions that warrant administrative attention. It consists of a set of standards for network management, including an Application Layer protocol, a database schema, and a set of data objects.RFC 3411 — An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks

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.

Overview and basic concepts

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 (see below) 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"). But the protocol also permits active management tasks, such as modifying and applying a new configuration. The managing system can retrieve the information through the GET, GETNEXT and GETBULK protocol operations or the agent will send data without being asked using TRAP or INFORM protocol operations. 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. The 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 is part of the Internet network management architecture. This architecture is based on the interaction of many entities, as described in the following section.

The Internet Management Model

As specified in Internet RFCs and other documents, a network management system comprises:

• Network elements -- Sometimes called managed devices, network elements are hardware devices such as computers, routers, and terminal servers that are connected to networks.
• Agents -- Agents are software modules that reside in network elements. They collect and store management information such as the number of error packets received by a network element.
• Managed object -- A managed object is a characteristic of something that can be managed. For example, a list of currently active TCP circuits in a particular host computer is a managed object. Managed objects differ from variables, which are particular object instances. Using our example, an object instance is a single active TCP circuit in a particular host computer. Managed objects can be scalar (defining a single object instance) or tabular (defining multiple, related instances).
• Management information base (MIB) -- A MIB is a collection of managed objects residing in a virtual information store. Collections of related managed objects are defined in specific MIB modules.
• Syntax notation -- A syntax notation is a language used to describe a MIB's managed objects in a machine-independent format. Consistent use of a syntax notation allows different types of computers to share information. Internet management systems use a subset of the International Organization for Standardization's (ISO's) Open System Interconnection (OSI) Abstract Syntax Notation (ASN.1) to define both the packets exchanged by the management protocol and the objects that are to be managed.
• Structure of Management Information (SMI) -- The SMI defines the rules for describing management information. The SMI is defined using ASN.1.
• Network management stations (NMSs) -- Sometimes called consoles, these devices execute management applications that monitor and control network elements. Physically, NMSs are usually engineering workstation-caliber computers with fast CPUs, megapixel color displays, substantial memory, and abundant disk space. At least one NMS must be present in each managed environment.
• Parties -- Newly defined in SNMPv2, a party is a logical SNMPv2 entity that can initiate or receive SNMPv2 communication. Each SNMPv2 party comprises a single, unique party identity, a logical network location, a single authentication protocol, and a single privacy protocol. SNMPv2 messages are communicated between two parties. An SNMPv2 entity can define multiple parties, each with different parameters. For example, different parties can use different authentication and/or privacy protocols.
• Management protocol -- A management protocol is used to convey management information between agents and NMSs. SNMP is the Internet community's de facto standard management protocol.