SNMP Reference Guide

40 Introduction
SNMP MIB OIDs
Each data class within an MIB is defined by an 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:
ROOT
CCITT(0)
ISO(
1)
ORG(
3)
DOD(
6)
INTERNET(
1)
MGMT(2)
MIB(1)
EXPERIMENTAL(3)
PRIVATE(
4)
ENTERPRISES(
1)
DELL(
674)
SNMPv2(6)