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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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17.1.5 The SNMP model<br />

The interaction between SNMP components is agent-restrictive: A manager can<br />

communicate only with an agent, <strong>and</strong> a subagent can communicate only with an<br />

agent. In no aspects of the model will a subagent communicate with a manager.<br />

If a manager needs to obtain or set the value of an object supported by a<br />

subagent, the request is delivered to the agent.<br />

The agent, upon realizing that the request is for an object in a MIB other than one<br />

it supports, attempts to find the object in one of the MIBs registered by a<br />

subagent. Upon finding the correct MIB, the agent passes the request to the<br />

subagent.<br />

The subagent then locates the correct value <strong>and</strong> passes it back to the SNMP<br />

agent. The agent then forwards this value back to the manager. This process, as<br />

well as the relationship that exists between manager, agents, <strong>and</strong> subagents, is<br />

illustrated in Figure 17-5 on page 636.<br />

SNMP Manager<br />

SNMP (as a communication<br />

protocol)<br />

Trap Response<br />

SNMP (as a communication<br />

protocol)<br />

SNMP Agent<br />

Get<br />

GetNext<br />

GetBulk<br />

Set<br />

SNMP<br />

DPI<br />

Figure 17-3 The SNMP model<br />

Register<br />

Reply<br />

MIB Query<br />

Reply<br />

Trap<br />

SNMP<br />

DPI<br />

SNMP sub-agent<br />

Chapter 17. Network management 633

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