Introduction to SNMP
Prerequisite: Observer Suite
SNMP Management Console is available in Observer Suite, bringing the cross-platform Simple Network Management Protocol (SNMP) standard to Observer .
Simple Network Management Protocol (SNMP) is not as simple as its name implies; it is a difficult concept to understand. This section provides a brief overview and description of SNMP, yet it is by no means a comprehensive tutorial. Ultimately, using Observer’s SNMP Management Console becomes easier with a basic understanding of how SNMP works.
Any network administrator, systems consultant, or network programmer will find SNMP Management Console useful. SNMP Management Console and its related utilities are designed to meet the needs of network professionals, ranging from beginner to expert.
Tip! SNMP Management Console is most useful for network administrators who want to monitor their LANs and manage SNMP-aware devices from a single location.
Simple Network Management Protocol (SNMP) is an application-layer protocol designed to facilitate the exchange of management information between network devices. The SNMP system consists of three parts: SNMP Manager, SNMP Agent, and MIB.
SNMP manager—uses information in the MIB to perform operations on each object.
SNMP agent—gathers data from the MIB, which is the repository for information about device parameters and network data. The agent also can send traps, or notifications of certain events, to the manager.
Management Information Base (MIB)—stores the information about each managed object.
From the perspective of a network manager, network management takes place between two major types of systems: those in control, called managing systems, and those observed and controlled, called managed systems. The most common managing system is called a Network Management System (NMS). Managed systems can include hosts, servers, or network components such as routers or intelligent repeaters.
Note: The exchange of information between managed network devices and a robust NMS is essential for reliable performance of a managed network. Because some devices have a limited ability to run management software, most of the computer processing burden is assumed by the NMS. The NMS runs the network management applications that present management information to network managers and other users.
Instead of defining a large set of commands, SNMP places all operations in a GetRequest, GetNextRequest, GetBulkRequest, and SetRequest format. For example, an SNMP manager can get a value from an SNMP agent or store a value in that SNMP agent. The SNMP manager can be part of a NMS, and the SNMP agent can reside on a networking device such as a router. If SNMP is configured on a router, the SNMP agent can respond to MIB-related queries being sent by the NMS.
 
Figure 59: SNMP simple diagram
 
GetRequest
supplies a list of objects and values they are to be set to (SetRequest). The agent returns GetResponse.
GetNextRequest
retrieves the next instance of information for a particular variable or device.
GetResponse
informs the management station of the results of the GetRequest or SetRequest by returning an error indication and a list of variable/value bindings.
GetBulkRequest
similar to GetNextRequest, but fills the GetResponse with up to a maximum repetition number of GetNext interactions.
SetRequest
alters the value of objects which can be written to the MIB.
Trap
an unsolicited message sent by an SNMP agent to an SNMP manager indicating that some event has occurred.
With this operation, an SNMP manager does not need to know the exact variable name. A sequential search is performed to find the needed variable from within the MIB.
In a managed device, specialized low-impact software modules, called agents, access information about the device and make it available to the NMS. Managed devices maintain values for several variables and report those, as required, to the NMS. For example, an agent might report such data as the number of bytes and packets in and out of the device, or the number of broadcast messages sent and received. In the Internet Network Management Framework, each of these variables is referred to as a managed object. A managed object is anything that can be managed, anything that an agent can access and report back to the NMS. All managed objects are contained in the Management Information Base (MIB), a database of the managed objects.
An NMS can control a managed device by sending a message to an agent of that managed device requiring the device to change the value of one or more of its variables. The managed devices can respond to commands such as set or get commands. The set commands are used by the NMS to control the device. The get commands are used by the NMS to monitor the device.