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<div class="CellBody"><a name="84005"> </a>Return a value</div>

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<div class="CellBody"><a name="84007"> </a><b class="command">set-request</b></div>

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<div class="CellBody"><a name="84009"> </a>Set a value</div>

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<div class="CellBody"><a name="84011"> </a><b class="command">trap</b></div>

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<div class="CellBody"><a name="84013"> </a>Event notification</div>

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<h4 class="EntityTitle"><a name="83620"><font face="Helvetica, sans-serif" size="-1" class="sans">Figure 3-4:&nbsp;&nbsp;SNMP Communication</font></a></h4>

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<h4 class="H3"><i><a name="83647">3.2.3  &nbsp;&nbsp;SNMP versions</a></i></h4>
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<dd><p class="Body"><a name="83648"> </a>SNMPv1 is defined by the following documents: RFC 1155, RFC 1157, and RFC 1212. SNMP version 2c (SNMPv2c) is not yet officially standardized as of this writing, though an IETF draft is available. In short, SNMPv2c improves upon SNMPv1 in the following ways:</p>
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<ul class="Bullet" type="disc"><li><a name="84073"> </a>The <b class="command">get-bulk</b> directive has been added for more efficient (less network-intensive) queries.</li></ul>
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<ul class="Bullet" type="disc"><li><a name="84077"> </a>Error codes have been expanded (see <a href="x-snmpErrors.html#83419"><i class="title">C.&nbsp;SNMP Errors</i></a>).</li></ul>
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<ul class="Bullet" type="disc"><li><a name="84081"> </a>Traps have been expanded (see <a href="c-agent7.html#83785"><i class="title">4.7&nbsp;Traps</i></a>).</li></ul>
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<h4 class="H3"><i><a name="83658">3.2.4  &nbsp;&nbsp;The Management Information Base</a></i></h4>
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<dd><p class="Body"><a name="83659"> </a>The Management Information Base (MIB) specifies a collection of management information on the agent that is controlled and monitored by an NMS. A MIB defines all the information an NMS can extract from the agent. For example, a MIB might specify that an agent will keep track of the number of errors that occur during the checksum of TCP packets.</p>
<dd><p class="Body"><a name="83660"> </a>As stated previously, the objects in the MIB are separate from the actual SNMP protocol. This allows the MIB information stored in a particular agent to be extended and customized without modification to the protocol.</p>
<dd><p class="Body"><a name="83661"> </a>The MIB that resides in an agent may be made up of several MIB modules. There are standard MIB modules and custom MIB modules. MIB-II is a standard MIB module that contains information about the Internet network protocol suite (TCP, UDP, IP, ICMP, and so on). For an example of the development of custom MIB module, see <a href="c-extend3.html#83539"><i class="title">6.3&nbsp;Compile-time MIB Extensions</i></a>.</p>
<dd><p class="Body"><a name="83667"> </a>For more information on available standard MIBs, see <a href="x-snmpRefList.html#83419"><i class="title">E.&nbsp;SNMP Reference List</i></a>. To explore the standard MIBs included with this component, examine the contents of the directory <b class="file">$WIND_BASE/target/src/snmpv1/mibs/*.mib</b> (also see <a href="c-agent2.html#85379"><i class="title">4.2.3&nbsp;$WIND_BASE/target/src/snmpv1/mibs/</i></a>).</p>
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<h4 class="H3"><i><a name="83673">3.2.5  &nbsp;&nbsp;The Structure of Management Information</a></i></h4>
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<dd><p class="Body"><a name="83674"> </a>Where the MIB defines the specific network management variables stored in an agent, the Structure of Management Information (SMI) specifies how these MIB variables are defined and identified. For example, the SMI places restrictions on the MIB variable types; only a handful of types are defined (integer, octet string, and so on).</p>
<dd><p class="Body"><a name="83675"> </a>The names used for MIB variables are taken from the object identifier (OID) name space administered by the ISO and CCITT. The name space is hierarchical, and authority for each part of the name space is subdivided at each level. <a href="c-background2.html#84284">Figure&nbsp;3-5</a> illustrates the object identifier name space hierarchy.&nbsp;<div class="frame">
<h4 class="EntityTitle"><a name="84284"><font face="Helvetica, sans-serif" size="-1" class="sans">Figure 3-5:&nbsp;&nbsp;Object Identifier Name Space</font></a></h4>

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<dd><p class="Body"><a name="84099"> </a>Objects are named according to the sequence of the numeric values on the nodes in the path from the root to the object. The string names provide a format more easily read by users. For example:<p class="table">
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<p class="BodyLeft"><a name="84102"> </a><b class="keyword">MIB-II</b> is</p>

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<p class="BodyLeft"><a name="84104"> </a>1.3.6.1.2.1</p>

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<p class="BodyLeft"><a name="84106"> </a><b class="file">iso.org.dod.internet.mgmt.mib</b></p>

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<p class="BodyLeft"><a name="84108"> </a><b class="keyword">WRS</b> is</p>

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<p class="BodyLeft"><a name="84110"> </a>1.3.6.1.4.1.731</p>

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<p class="BodyLeft"><a name="84112"> </a><b class="file">iso.org.dod.internet.private.enterprises.WRS</b></p>

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<dd><p class="Body"><a name="84083"> </a></p>
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