Using Subagents

Using subagents with an extensible SNMP agent avoids the problem of having one very large SNMP agent. Before subagents were devised, an SNMP agent had to be recompiled to add new management objects in MIBs. The subagent approach provides the ability to dynamically add management objects to an agent without recompiling the agent. The need to standardize the way in which agents and subagents work together led to the development of the AgentX protocol.

AgentX Protocol

The AgentX protocol enables subagents to connect to the master agent. The protocol also enables the master agent to distribute received SNMP protocol messages to the subagents.

The AgentX protocol defines an SNMP agent to consist of one master agent entity and other subagent entities. The master agent runs on the SNMP port, and sends and receives SNMP messages as specified by the SNMP framework documents. The master agent does not access the subagents' management information directly. The subagents do not handle SNMP messages, but subagents do access their management information. In short, the master agent handles SNMP for the subagents, and only handles SNMP. The subagent handles manipulation of management data but does not handle SNMP messages. The responsibilities of each type of agent are strictly defined. The master agent and subagents communicate through AgentX protocol messages. AgentX is described in detail by RFC 2741. See http://www.ietf.org/rfc/rfc2741.txt

The SMA performs in the role of the master agent. Subagents that you create can add management objects to the agent.

Functions of a Subagent

An AgentX subagent performs the following functions:

• Initiates AgentX sessions with the master agent

• Registers MIB regions with the master agent

• Instantiates managed objects

• Binds object IDs (OIDs) within its registered MIB regions to actual variables

• Performs management operations on variables

• Initiates notifications, or traps