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Understanding the network.pdf - Back to Home

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Figure 11.2. The MIB hierarchy.<br />

The "<strong>to</strong>p" of <strong>the</strong> MIB is <strong>the</strong> root of <strong>the</strong> tree. The SMI specifies that MIBs contain<br />

information about <strong>the</strong>ir crea<strong>to</strong>r, version, and any dependency on o<strong>the</strong>r MIBs for<br />

<strong>the</strong>ir functionality, etc. The MIB's interrelated managed objects are grouped<br />

<strong>to</strong>ge<strong>the</strong>r in<strong>to</strong> object-groups. Each object-group has its own MIB-unique identifier.<br />

Additionally, each of <strong>the</strong> managed objects in <strong>the</strong> object-group each has its own<br />

object-identifier (OID). The objects <strong>the</strong>mselves can be ei<strong>the</strong>r scalar or tabular.<br />

Scalar objects are typically simple ASN.1 data types that contain a single value or<br />

instance. Data variables contained in managed objects are referred <strong>to</strong> as instances.<br />

Scalar object instances use an instance identifier of ".0" <strong>to</strong> identify <strong>the</strong>mselves.<br />

Tabular objects can contain one or more data instances. When requesting an object<br />

that contains multiple instances, <strong>the</strong> instance identifier ".1" is used. With tabular<br />

objects, <strong>the</strong> INDEX clause defines what <strong>the</strong> instance identifier is for each of <strong>the</strong><br />

tabular data values.<br />

The MIB module's type indicates its use and its identification in <strong>the</strong> global MIB<br />

naming mechanism. Standard type MIB modules are defined by standards bodies<br />

(mainly IETF/IAB) for <strong>the</strong> management of standards-based services and functions.

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