Understanding the network.pdf - Back to Home

sequential order. It provides a means of retrieving tabular data nested in the
MIB that cannot be directly accessed through the use of the Get operation.
• SetRequest—The Set command is used by the management station to issue
change commands to the managed device. Set commands can only be
issued to change settings defined in the managed device's MIB. Additionally,
they must be issued by a management station that has a community name
defined for read and write access.
• GetResponse— GetResponse commands are used by the agent running on
the managed device to send responses to the management station's Get and
GetNext commands.
• Trap— Trap messages are unsolicited messages sent from the managed
device to the management station. Part of the agent configuration is the
definition of the host(s) to send Trap messages. These messages are used to
relay the occurrence of specifically defined events such as a link failure or
reboot.
With the addition of SNMP v2 authentication, access control, and
manager-to-manager data exchange capabilities, SNMP v2 also added two
management station request operations:
• GetBulkRequest—The GetBulkRequest operation is used by the
management station in a manner similar to the GetNextRequest, except
that GetBulkRequest is much more efficient. GetBulkRequest allows the
management station to request management data recursively from the
relative position of the last GetRequest, without any data size specification.
As much data will be sent as can fit in the PDU. With the GetNextRequest
command, the data size needs to be specified along with the request, so if
actual data size exceeds the specified size, there can be errors. This
command was added to accommodate data extraction from large table sizes,
which were implemented in SNMP v2.
• InformRequest—This command was developed to allow communication
between management stations. With the InformRequest command,
management stations can send Trap messages to each other about locally
monitored events. This facility enables distributed local management
stations to monitor local networks, which in turn relay management data and
events to a master network management station.
With SNMP, the message is the management. The agents and management stations
are merely command and control interpreters. They perform collection and display
functions, but the actual management is all performed using SNMP. To this end, all
data request and responses must be made using specific network layer addressing.
SNMP agents do not blindly start sending SNMP messages after the device is
functioning. Management data must be requested by a verifiable host with the
proper access credentials. Management stations that support SNMP v1 and SNMP v2
do data verification to determine which SNMP version is supported by the agent.