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Once you have enabled the subagent, you can start, stop or restart it from the
SNMP Subagent Control page or the Services Control Panel for Windows
NT/Windows 2000.
NOTE
Understanding SNMP Messages
GET and SET are two types of messages defined by SNMP. GET and SET messages
are sent by a network management station (NMS) to a master agent. You can use
one or the other or both with the Administration Server.
SNMP exchanges network information in the form of protocol data units (PDUs).
These units contain information about variables stored on the managed device,
such as the web server. These variables, also known as managed objects, have
values and titles that are reported to the NMS as necessary. Protocol data units sent
by the server to the NMS are known as "traps." The use of GET, SET, and "trap"
messages are illustrated in the following examples.
NMS-initiated Communication. The NMS either requests information from the
server or changes the value of a variable store in the server's MIB. For example:
The NMS sends a message to the Administration Server master agent. The
1.
message might be a request for data (a GET message) or an instruction to set a
variable in the MIB (a SET message).
The master agent forwards the message to the appropriate subagent.
2.
The subagent retrieves the data or changes the variable in the MIB.
3.
The subagent reports data or status to the master agent, and then the master
4.
agent forwards the message back (a GET message) to the NMS.
The NMS displays the data textually or graphically through its network
5.
management application.
Server-initiated Communication. The server subagent sends a message or "trap"
to the NMS when a significant event has occurred. For example:
The subagent informs the master agent that the server has stopped.
1.
The master agent sends a message or "trap" reporting the event to the NMS.
2.
After making any SNMP configuration changes, you must click the Apply
button, then restart SNMP subagent.
Understanding SNMP Messages
Chapter 10
Monitoring Servers
241
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