SNMP Reference Guide

Introduction 37
Management Actions
Management actions can be performed using the SNMP Set command.
These actions can consist of configuring a phone number for the system’s
owner, rebooting a system, or changing the asset tag of the system. See the
previous section, "SNMP Security" on page 36, for limitations on Set
operations.
SNMP Traps
SNMP is frequently used to monitor systems for fault conditions such as
temperature violations, hard drive failures, and so on. Management
applications can monitor for these conditions by polling the appropriate
OIDs with the Get command and analyzing the returned data. This method
has its drawbacks. If it is done frequently, significant amounts of network
bandwidth can be consumed. If it is done infrequently, the response to the
fault condition may not occur in a timely fashion. SNMP traps avoid these
limitations of the polling method.
An SNMP trap is an asynchronous event indicating that something
significant has occurred. This is analogous to a pager receiving an important
message, except that the SNMP trap frequently contains all the information
needed to diagnose a fault.
Two drawbacks to SNMP traps are that they are sent using UDP, which is not
a guaranteed delivery mechanism, and that they are not acknowledged by
the receiver.
An SNMP trap message contains the trap’s enterprise OID, the agent IP
address, a generic trap ID, the specific trap ID, a time stamp, and zero or
more variable bindings (varbinds). The combination of an enterprise OID
and a specific trap ID uniquely identifies each Server Administrator-defined
trap. A varbind consists of an OID and its value and provides additional
information about the trap.
In order for a management system to receive SNMP traps from a managed
system, the node must be configured to send traps to the management
system. Trap destination configuration is dependent on the operating system.
When this configuration is done, a management application on the
management system can wait for traps and act on them when received.
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