SNMP key terms
- Simple Network Management Protocol. A set of standards for communication with devices connected to a TCP/IP network, widely accepted as the de facto standard for network management. Examples of these devices include routers, hubs, servers and switches. Software for managing devices via SNMP is available for every kind of commonly used computer and is often bundled along with the device they are designed to manage
- SNMP compatible
- A device is said to be "SNMP compatible" if it can be monitored and/or controlled using SNMP messages. Devices that are SNMP compatible contain SNMP "agent" software. An SNMP Agent is an application running on the device that performs the operational role of receiving and processing SNMP messages, sending responses to the SNMP manager, and sending traps when an event occurs.
- SNMP Manager
- An SNMP Manager or SNMP Service is an application that performs the operational roles of generating SNMP messages/requests to modify and retrieve management information, and receiving the requested information and trap-event reports that are generated by the SNMP agent. Monitor one is an SNMP Manager!
- SNMP Messages
- The most commonly used SNMP versions are SNMPv1 and SNMPv2. SNMPv1 defines five operation types: GetRequest, GetNextRequest, SetRequest, GetResponse and Trap. SNMPv2 defines an additional type: GetBulk. The SNMP agent responds to a received request by sending a GetResponse message. If a predefined condition or an extraordinary event occurs, the SNMP agent can also send a Trap message to the SNMP Manager system.
An SNMP message is build upon several fields from which the most important ones are: the operation type and (one or more repeating groups of) an Object identifier string and a value. An Object Identifier string consists of an Object Identifier and an Instance and is used to uniquely identify SNMP agent fields.
- Object Identifier (OID)
- An Object Identifier is the identification value of an object that is defined in a MIB. Object identifiers are arranged in a hierarchical tree structure (MIB tree) that is compliant with Internet standard and that consists of roots and branches. An object identifier is written as a sequence of sub-identifiers, starting with the tree root, in dotted decimal notation. For example, the Cisco branch of the MIB naming tree is expressed as 184.108.40.206.4.1.9
- An instance specifies the row in which an object that is part of a table is located. The instance is appended to the object identifier and has a format that is similar to the latter. For objects that are not part of a table, the instance is zero (.0)
- A Management Information Base (MIB) is a schema or blueprint that contains the hierarchical order of all of the managed objects. Each managed object has a unique identifier (OID) and includes the type (such as counter, string, gauge, or address), access level (such as read/write), size restrictions, and range information of the object.
Below is a snapshot of (a part of) the Monitor one MIB tree.
The snapshot shows the "system" and the "interfaces" branches. Both compiled from the MIB file defined by rfc1213.