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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
           9  TCP/IP Network Management Framework and Protocols (SNMP and RMON)
                9  TCP/IP Structure of Management Information (SMI) and Management Information Bases (MIBs)

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TCP/IP Structure of Management Information (SMI) and Management Information Bases (MIBs) Overview
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TCP/IP MIB Object Descriptors and Identifiers and the Object Name Hierarchy and Name Notation
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TCP/IP MIB Objects, Object Characteristics and Object Types
(Page 2 of 4)

Syntax

An object’s Syntax defines its data type and the structure that describes it. This attribute of an MIB object is very important because it defines the data type of information that the object contains. There are two basic categories of data types allowed:

  • Regular Data Types: These are single pieces of information, of the type we are used to dealing with on a regular basis; examples would be integers or strings. These are called base types in SMIv2. SMIv1 differentiates between primitive types like integers defined in ASN.1, and defined types that are special forms of primitive types that are still single pieces of information but with certain special meaning attached to how they are used. SMIv2 doesn't use those two terms.

  • Tabular Data: A collection of multiple data elements. This may take the form of a list of base types or a table of base types. For example, a table of integers could be constructed to represent a set of values. In SMIv1 these are called constructor types; in SMIv2 they are conceptual tables. They can be accessed using special SNMP mechanisms designed for reading tables. See the topic on SNMP table traversal for more on tables.
Access (Max-Access in SMIv2)

This field defines the ways that an SNMP application will normally use the object. In SMIv1, there are four different possible values: read-only, read-write, write-only, and not-accessible.

In SMIv2 there are five values, which are described as a hierarchy of sorts. SMIv2 calls this characteristic Max-Access (maximum access) to make it explicit that higher access levels include the lower levels as well. For example, an object with read-create access can also be used in any of the modes “below it”, such as read-write, but not vice versa. Table 205 shows the five SMIv2 access values, in decreasing order of access. Note that write-only has been removed in SMIv2:


Table 205: SNMP SMI Version 2 Max-Access Values

Max-Access Value

Description

read-create

Object can be read, written or created.

read-write

Object can be read or written.

read-only

Object can only be read.

accessible-for-notify

Object can be used only using SNMP notification (SNMP traps).

not-accessible

Used for special purposes.


Status

Indicates the currency of the object definition. In SMIv1 there are three values: mandatory, optional and obsolete. In SMIv2, the first two are combined into simply current, meaning a current definition. The value obsolete is retained, and deprecated is added, meaning the definition is obsolete but maintained for compatibility.

Definition (Description in SMIv2)

A textual description of the object.

Key Concept: Each management information variable, called a MIB object, has associated with it five key attributes: its name, syntax, maximum access, status and definition. It may also have a number of optional characteristics.



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TCP/IP Structure of Management Information (SMI) and Management Information Bases (MIBs) Overview
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TCP/IP MIB Object Descriptors and Identifiers and the Object Name Hierarchy and Name Notation
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Version 3.0 - Version Date: September 20, 2005

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