3.1.6 Trap Notification
The subagents send the traps to the Master Agent; the Master Agent the decides which managers will receive the trap. This decision is configurable.
3.2 Description of the Subagent
Subagents do not interact with the network manager directly. Instead, they communicate with the Master Agent. The management responsibility of the subagent can be offered to the Master Agent; however, it is up to the Master Agent to accept or ignore the offers.
After the subagents have registered with the Master Agent, they wait for the SNMP requests from the Master Agent. If a request is received, it sends the appropriate response. Additionally, the subagents can send SNMP traps.
The subagent is composed of four major components: the SNMP driver, Service API stack, subagent application, and MIB database. The Master Agent is responsible for receiving and sending the SNMP Protocol Data Units (PDUs). It also encodes and decodes the PDUs. The SP (Stack) dispatches the received requests appropriately or calls the applicable call back functions.
The system interface module is the implementation of the call back) of all the variables managed by the subagent. The MIB compiler automatically generates this information.
Except for the system dependent interface and the MIB database, the other components are reusable by other subagents and are provided in a library.
3.2.1 Establishment
This step involves the effort by the subagents to announce their presence and describe how to communicate with them. The transport used is UDP. The port on which the subagents listen for the SNMP request is configurable, as mentioned in "4.4 Agents Access Control File" on "4.4 Agents Access Control File". This establishment can also be done dynamically through a handshaking protocol.
3.2.2 Maintenance
The subagent periodically checks for existence of the Master Agent. The dynamic subagents (not invoked by the Master Agent) periodically determine whether the Master Agent is active. The runtime library reregisters the subagent's subtree with the Master Agent in the event of any interruptions.
3.2.3 Termination
Termination involves the effort to inform the Master Agent that the dynamic agent is about to exit. The Master Agent can then remove the row entry from its subagent table in the memory.
3.3 Using the Master Agent
snmpdx [-h] [-p port_number] [-r filename] [-a filename] [-c dirname] [-i filename] [-o filename] [-y] [-m GROUP|SPLIT] [-d debug_level] |
The command line arguments are shown in Table 3-2.
Table 3-2 Master Agent Command Line Arguments
Argument | Description |
|---|---|
-a filename | A full path (default) of the access control file is: /etc/snmp/conf/snmdx.acl; see "4.4 Agents Access Control File" for more information |
-c dirname | The full path of the (default) directory containing the agent resource files; the default directory is: /etc/snmp/conf |
-d debug_level | Used for debugging purposes; depending on the debug_level (0-4), it prints a specific amount of information; the default debug_level is 0 |
-h | Command usage |
-i filename | The full path of the PID used by the Master Agent for recovery after a crash; it contains tuples of the UNIX process ID, port number, resource name, and agent name (default files) is: /var/snmp/snmpdx.st |
-o filename | This file contains the tuple (enterprise_name, oid); for example, (Sun Microsystems,1.3.1.6.1.4.32); the file (default) is used as a base for lookup in the trap-filtering and forwarding process is: /etc/snmp/conf/enterprises.oid |
-m GROUP | SPLIT | The forwarding of SNMP requests mode; the default is GROUP; see "3.1.5 Sending Requests" for a description of the two modes |
-p port_number | The port number; the default port number is 161; for example, -p 1234 |
-r filename | The full path of the resource file name used by the Master Agent; stores information about the subagents that the Master Agent invokes and manages; the default resource file is /etc/snmp/conf/snmpdx.rsrc; see "4.2 Agents Resource Configuration Files" for more information |
-y | A recovery indicator signals when invoking the Master Agent process and then invokes the recovery module; the recovery process discovers which subagents in the previous session are still active; those subagents not active are re-spawned by the Master Agent |