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 these messages 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 following examples show the use of GET, SET, and trap messages in communication initiated by the NMS or by the server.

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:

1. The NMS sends a message to the Administration Server master agent. The message might be a request for data (a GET message), or an instruction to set a variable in the MIB (a SET message).

2. The master agent forwards the message to the appropriate subagent.

3. The subagent retrieves the data or changes the variable in the MIB.

4. The subagent reports data or status to the master agent, and then the master agent forwards the GET message back to the NMS.

5. The NMS displays the data textually or graphically through its network management application.

   Server-initiated Communication. The server subagent sends a message or trap to the NMS when a significant event has occurred. For example:

6. The subagent informs the master agent that the server has stopped.

7. The master agent sends a message or trap reporting the event to the NMS.

8. The NMS displays the information textually or graphically through its network management application.