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iso.identfied-orgnaization.dod.internet.mgmt.1.1.4.0<br />

In <strong>the</strong> ISO/ITU-T scheme, <strong>the</strong> management subtree is where all <strong>the</strong> IETF/IAB<br />

standard MIB modules reside. The experimental subtree contains all of <strong>the</strong><br />

in-process MIB modules. The private.enterprises subtree contains all of <strong>the</strong> cus<strong>to</strong>m<br />

MIB modules created by device manufacturers, management station vendors, and<br />

software developers. Each MIB developer is assigned a subtree ID. This ID serves as<br />

<strong>the</strong> root location vendor's MIB.<br />

NOTE<br />

Most SNMP managers and some agent implementations provide a MIB "walking"<br />

<strong>to</strong>ol that allows you <strong>to</strong> browse MIB modules. The <strong>network</strong> management <strong>to</strong>ols section<br />

lists some of <strong>the</strong> available <strong>to</strong>ols.<br />

The SNMP Message Formats<br />

The SNMP message is used <strong>to</strong> transport <strong>the</strong> BER-encoded, SMI-defined ASN.1<br />

objects and values. The message has two parts: <strong>the</strong> message header (see Figure<br />

11.4) and <strong>the</strong> SNMP PDU. SNMP v1 and SNMP v2 use <strong>the</strong> same message header<br />

formats (see Figure 11.5), but different PDUs. The SNMP v1 SMI defines a PDU for<br />

data operations and for Trap operations (see Figure 11.6). The SNMP v2 SMI defines<br />

a single PDU for both data and Trap operations and a separate PDU (see Figure 11.7)<br />

for <strong>the</strong> GetBulkRequest operation. First, let's examine <strong>the</strong> SNMP v1 and v2<br />

message header. Then, we will examine <strong>the</strong> various SNMP message and Trap PDU<br />

formats.<br />

Figure 11.4. SNMP v1 and SNMP v2 message headers.

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