System information

330 Observer Suite: SNMP Management
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.
• 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 a number of 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.
Network Management
Station — SNMP Manager
Network Device — MIB
SNMP Agent
GetResponse, Trap
GetRequest, GetNextRequest,
GetBulk, SetRequest