The initial version of SNMP, SNMPvl is defined in RFC 1157, Simple Network Management Protocol (SNMP). The protocol's simplicity is apparent by the set of operations that are available. Figure 3-27 shows the basic SNMP messages, which the manager uses to transfer data from agents that reside on managed devices. These messages are described as follows:
■ Get Request: Used by the manager to request a specific MIB variable from the agent.
■ Get Next Request: Used after the initial get request to retrieve the next object instance from a table or list.
■ Set Request: Used to set a MIB variable on an agent.
■ Get Response: Used by an agent to respond to a manager's Get Request or Get Next Request message.
■ Trap: Used by an agent to transmit an unsolicited alarm to the manager. A Trap message is sent when specific conditions occur, such as a change in the state of a device, a device or component failure, or an agent initialization or restart.
Figure 3-27 SNMPv1 Message Types
Retrieve Value of Specific MIB Variable
Get Next Request Retrieve Next Issuance of MIB Variable
Set Request Modify the Value of a MIB Variable
Contains Values of Requested Variable
Transmits an Unsolicited Alarm Condition
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