Each data class within a Management Information Base (MIB) is defined
by an Object Identifier (OID). OIDs are unique across all MIBs. An
OID consists of a series of digits separated by periods. The OID functions
in a similar fashion to a phone number. The phone number 011-512-471-0000
uniquely identifies a single phone. The phone number can be broken
down into a number of components to uniquely identify a phone. The
first component, 011, is the country code for the United States. The
second component, 512, identifies the area code for central Texas.
The third component, 471, is the phone exchange for a large state
university in the city of Austin. The final component, 0000, is the
main switchboard.
There are two main differences between the phone number example
and an actual OID. The first difference is that there are many more
components in an OID, up to 128. The combination of these components
is called an OID prefix. The second difference is that OIDs support
the concept of indexes or keys. The OID prefix specifies the data
class but does not specify an instance of the data within the class.
Indexes can be used to identify the instances of a data class. These
indexes are referred to as the OID suffix.
The assignment of values for each OID prefix component can be illustrated
by using a tree structure. The following is an example of an OID assignment:
Table 1. ROOT.
This table lists the ROOT information
CCITT(0) |
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ISO(1) |
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ORG(3) |
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DOD(6) |
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INTERNET(1) |
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MGMT(2) |
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MIB(1) |
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EXPERIMENTAL(3) |
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PRIVATE(4) |
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ENTERPRISES(1) |
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DELL (674) |
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SNMPv2(6) |
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In the preceding example, the OID prefix for the Dell enterprise
would be 1.3.6.1.4.1.674.
The numbers in boldface type show the categories and numbers that
apply to Server Administrator. All Server Administrator-defined OIDs
consist of 1.3.6.1.4.1.674 followed by additional component values.