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TCP/IP MIB Objects, Object Characteristics and Object Types
(Page 2 of 4)
Syntax
An objects 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
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Description
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read-create
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Object can be read, written or
created.
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read-write
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Object can
be read or written.
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read-only
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Object can only be read.
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accessible-for-notify
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Object can
be used only using SNMP notification (SNMP traps).
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not-accessible
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Used for special purposes.
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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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Version 3.0 - Version Date: September 20, 2005
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