Creating a Subagent Using the eSNMP API
3.2 The Structure of Management Information
3.2.1 Assigning Object Identification Codes
Each object in a MIB is associated with an identifier of the ASN.1 type, called
an object identifier (OID). OIDs are unique integers that follow a hierarchical
naming convention.
Each OID has two parts:
•
A preassigned portion that is always represented on the SMI tree as 1.3.6.1
or iso (1), org (3), dod (6), Internet (1).
•
A developer-assigned portion for the private development of MIBs.
Note
Your organization may require you to register all newly assigned OIDs.
In addition to an OID, you should also assign a name to each object to help with
human interpretation.
3.2.2 MIB Subtrees
Understanding MIB subtrees is crucial to understanding the eSNMP API and
how your subagent will work.
Note
This manual assumes that you understand the OID naming structure
used in SNMP. If not, refer to RFC 1902: Structure of Management
Information for Version 2 of the Simple Network Management Protocol
(SNMP Version 2).
The information in SNMP is structured hierarchically like an inverted tree. Each
node has a name and a number. Each node can also be identified by an OID,
which is a concatenation of the subidentifiers (nonnegative numbers). These
numbers are on the path from the root node down to that node in the tree. In
this hierarchy, data is associated only with leaf nodes. (A leaf node represents a
MIB variable that can have an instance and an associated value.)
An OID must be at least two subidentifiers and at most 128 subidentifiers in
length. The subidentifier ranges are:
•
Subidentifier 1 values range from 0 to 2, inclusive.
•
Subidentifier 2 values range from 0 to 39, inclusive.
•
The remaining subidentifier values can be any nonnegative number.
Figure 3–1 illustrates the SMI hierarchical tree arrangement as specified in RFCs
1155 and 1902.
3–2 Creating a Subagent Using the eSNMP API
