TCP/IP Tutorial and Technical Overview - IBM Redbooks

As an example, consider the object ifType, defined by RFC 2863. ifType is part of
the Interface group defined by RFC 1213. Its SMIv2 definitions is illustrated in
Figure 17-1.
ifType OBJECT-TYPE
SYNTAX IANAifType
MAX-ACCESS read-only
STATUS current
DESCRIPTION
“The type of interface. Additional values for ifType are
assigned by the Internet Assigned Numbers Authority
(IANA), through updating the syntax of the IANAifType
textual convention.”
::= { ifEntry 3 }
Figure 17-1 SMIv2 definition of sysUpTime
Object identifiers (OIDs)
A managed object not only has to be described but identified, too. This is done
using the ASN.1 object identifier (OID). The object identifier reserves a set of
numbers for different groups. Each object is identified by a string of numbers
indicating the hierarchy to which it belongs. Referring back to the example of
ifType, this object has an OID of 1.3.6.1.2.1.2.2.1.3. This can initially be broken
into two parts:
ifEntry 1.3.6.1.2.1.2.2.1
ifType 3
Note that the terms ifType, 1.3.6.1.2.1.2.2.1.3, and ifEntry.3 are functionally
interchangeable. However, ifType’s OID can be further broken down as follows:
ifTable 1.3.6.1.2.1.2.2
ifEntry 1
ifType 3
Again, the terms ifType, 1.3.6.1.2.1.2.2.1.3, ifTable.1.3, and ifEntry.3 are all
functionally interchangeable. The OID can continue to be broken down because
each digit has a specific meaning. The significance of each digit adheres to the
following rules:
► The first digit defines the node administrator:
– 1 for ISO
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