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SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration (Mani-Chandy, 1985). These variables can then be queried (and sometimes set) by managing applications. In typical SNMP uses, one or more administrative computers, called managers, have the task of monitoring or managing a group of hosts or devices on a computer network. Each managed system executes, at all times, a software component called an agent which reports information via SNMP to the manager.
Essentially, SNMP agents expose management data on the managed systems as variables. The protocol also permits active management tasks, such as modifying and applying a new configuration through remote modification of these variables. The variables accessible via SNMP are organized in hierarchies (Mansouri-Samani, 1992). These hierarchies, and other metadata (such as type and description of the variable), are described by Management Information Bases (MIBs).
An SNMP-managed network consists of three key components:
A managed device is a network node that implements an SNMP interface that allows unidirectional (read-only) or bidirectional access to node-specific information. Managed devices exchange node-specific information with the NMSs. Sometimes called network elements, the managed devices can be any type of device, including, but not limited to, routers, access servers, switches, bridges, hubs, IP telephones, IP video cameras, computer hosts, and printers.
An agent is a network-management software module that resides on a managed device. An agent has local knowledge of management information and translates that information to or from an SNMP specific form.
A network management system (NMS) executes applications that monitor and control managed devices. NMSs provide the bulk of the processing and memory resources required for network management. One or more NMSs may exist on any managed network.
In conditions such as extreme weather or temporary inaccessibility that pose a difficult challenge to maintaining the performance of the equipment, a reliability assessment must be done to understand the impact that a component failure has on other components as well as the whole system. This will also help determine how many spares of each component are needed.