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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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To illustrate the process of querying an object using SNMP, refer back to the<br />

example of the ifType object. Figure 17-5 illustrates the sequence of events<br />

occurring when executing a getNext request for the ifType object.<br />

SNMP<br />

Manager<br />

getNext ifType<br />

(UDP,Port 161)<br />

ifType.1 = 6<br />

(UDP, manager's<br />

ephemeral port)<br />

Figure 17-5 An example of SNMP manager, agent, <strong>and</strong> subagent interaction<br />

The sequence of events is as follows:<br />

1. In this example, a getNext request is executed by the SNMP manager for<br />

ifType.<br />

2. The SNMP agent does not recognize ifType as an object from the System<br />

Group or SNMP Group MIBs. It does, however, recognize ifType as an object<br />

from a MIB registered by a subagent. In this case, the MIB is the Interface<br />

Group MIB, <strong>and</strong> was registered by the <strong>TCP</strong>/<strong>IP</strong> subagent.<br />

3. The SNMP agent passes the getNext over the DPI socket to the <strong>TCP</strong>/<strong>IP</strong><br />

subagent.<br />

4. The subagent recognizes ifType as an object in the Interface MIB <strong>and</strong> obtains<br />

the next object with a valid value: ifType.1.<br />

5. The subagent sends a response back to the agent with the object ifType.1<br />

<strong>and</strong> the value 6 (which, by RFC definition, is Ethernet).<br />

6. The agent then replies back to the manager, again indicating that the object is<br />

ifType.1 <strong>and</strong> the value is 6.<br />

636 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

SNMP<br />

Agent<br />

ifType belongs to the<br />

Interface Group,<br />

which was registered<br />

by the <strong>TCP</strong>/<strong>IP</strong><br />

sub-agent<br />

Forward this value<br />

to the requesting<br />

manager<br />

MIBs registered<br />

by sub-agents<br />

System Group<br />

MIB<br />

SNMP Group<br />

MIB<br />

getNext ifType<br />

(DPI socket)<br />

ifType.1 = 6<br />

(DPI socket)<br />

<strong>TCP</strong><strong>IP</strong><br />

Sub-agent<br />

Retrieve from the<br />

Interface Group MIB<br />

ifType.1 = 6<br />

Interface Group<br />

MIB<br />

ifType.1 = 6<br />

ICMP Group MIB<br />

<strong>TCP</strong> Group MIB<br />

UDP Group MIB<br />

<strong>IP</strong>Group MIB

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