SNMP - Overview
- Kelli Higdon
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SNMP (Simple Network Management Protocol) was designed as the standard language to be used by all computers on a network. The SNMP protocol is used by network management systems to communicate with network elements to monitor and control different aspects of the equipment. In an SNMP operation, network information is exchanged through messages sent between the Manager and Agent. The Manager uses messages to request operations to be performed on the SNMP agent. The messages sent are GetRequest, GetNextRequest, SetRequest, and GetBulk. The SNMP Agent responds with a GetResponse message. If a specific condition or event occurs the SNMP Agent sends a Trap message to the Manager for viewing. The SNMP Manager and the SNMP Agent are described below.
SNMP Manager: An SNMP Manager is an application that performs the operational roles of generating requests to modify and retrieve management information and receiving the requested information and trap-event reports that are generated by the SNMP agent. SNMP management applications such as Castlerock (SNMPC), and AdRem can be used and have been verified to operate on the IMG 2020. The IMG 2020 is however is not limited to the SNMP manager applications mentioned. Other applications can be utilized, but the applications mentioned have been verified.
SNMP Agent: An SNMP Agent is an application that performs the operational role of receiving and processing requests, sending responses to the manager, and sending traps when an event occurs. The IMG 2020 acts as an SNMP Agent.
Below are descriptions of messages sent between the Manager and Agent.
SNMP Trap: Message which is initiated by an SNMP Agent and sent to the SNMP Manager. For example, the IMG 2020 (SNMP Agent) could send a message to the SNMP Manager that one of its spans has failed. This is termed an SNMP Trap. Basically, it is an alarm telling the Manager that a span is out of service
SNMP Get: Message which is initiated by the SNMP Manager when it wants to retrieve some data from an SNMP Agent. For example, the SNMP Manager might query the IMG 2020 for span status every 2 minutes. From the data retrieved via the IMG 2020, the SNMP manager could create a chart of Out of Service versus In Service, which would give the operator an idea of network quality.
SNMP SET: (Not Supported on the IMG 2020) Message which is initiated by the SNMP Manager that is sent when the operator wants to change data on a network element. For example, the operator could change a system (SNMP Agent) operating parameter.
Each message sent between the SNMP Agent and the SNMP Manager makes reference to a specific object. For example, requesting span status is requesting the status of the object which is a span. These objects have an address or number associated with them. The number is referred to as an OID (Object Identifier). A series of OIDs in a specific area are considered the MIB (Management Information Base). Below is a description of what a MIB is.
MIB: A Management Information Base (MIB) is a scheme that contains the hierarchical order of all of the managed objects. Each managed object in an MIB has a unique identifier. The identifier includes the type (such as counter, string, gauge, or address), access level (such as read/write), size restrictions, and range information of the object. The MIB is extensible, which means the manufacturer can append information to an object to extend the tree as much as needed. These new MIB definitions must be added both to the SNMP Agent and to the SNMP Manager (NMS).
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