Reference Guide

Introduction 19
SNMP Master Agent
Typically, the SNMP agent on a managed system consists of one SNMP master agent and zero or more SNMP
extension agents. This SNMP agent extendable structure facilitates the addition of new MIB modules
without having to rebuild the entire SNMP agent and is invisible to SNMP management applications.
The SNMP master agent is responsible for receiving SNMP request protocol messages from SNMP management
applications and sending SNMP response protocol messages. As part of processing SNMP request
protocol messages, the SNMP master agent typically communicates with one or more SNMP extension
agents. This communication does not involve standard SNMP protocol messages. The SNMP master
agent uses an extension protocol that shields the SNMP extension agent from the standard SNMP
protocol messages. The extension protocol also provides a way for SNMP extension agents to send SNMP
event notifications (called traps in SNMPv1). The SNMP master agent is also responsible for sending
SNMP event notification protocol messages to SNMP management applications.
On supported operating systems, the SNMP master agent is provided with the operating system.
For example, on supported Microsoft
®
Windows
®
operating systems, the Windows SNMP service is the
SNMP master agent. For information on the versions of the SNMP protocol supported by the SNMP
master agent, see the operating system documentation.
SNMP Extension Agent
The SNMP extension agent is responsible for registering the MIB objects that it supports with the
SNMP master agent and then processing requests from the SNMP master agent for those MIB objects.
The SNMP extension agent also initiates event notifications to the SNMP master agent. The SNMP
extension agent does not receive or send standard SNMP protocol messages. The SNMP extension agent
communicates with the SNMP master agent using an extension protocol defined by the SNMP master agent.
The Server Administrator SNMP subagent is an SNMP extension agent.
Managed Object
A managed object is any item in a computer system that can be singled out for discovery, monitoring,
or user intervention and correction.
NOTE: Not all managed objects described in this guide are supported by all systems.
MIB
A MIB acts as a structured road map for managed objects. As an Application Programming Interface
(API), a MIB allows systems management tools to retrieve data maintained by an agent. The server
administrator MIB is divided into several major groups of managed objects.