Any communication from subagents to the Master Agent is done through UDP port 161. The topic of sending traps to the Master Agent from the subagents is discussed in "3.1.6 Trap Notification".
The Master Agent communicates on separate ports for each subagent.
The Master Agent also checks to be sure that registered subagents are up and running, based on the following conditions:
No activity between the Master Agent and the subagents. The Master Agent (based on watch_dog time as defined in the agent resource file) is used to determine whether a particular subagent is active. This is accomplished by sending an SNMP Get request to the subagent if there has been no activity between the subagent and the Master Agent for some specific configured period of time.