Connectivity Guide

Standards for writing MIBs are defined by the Internet Engineering Task Force (IETF). Structure of Management Information (SMI) is a
standard that specifies the rules for defining the structure and type of managed objects and events in a MIB. SMIv1 is specified in Request
For Comments (RFC) 1155. The Server Administrator MIB conforms to the SMIv1 standard.
SNMP is a systems management standard originally designed for network management. SNMP manages much more than networks.
Information Technology (IT) professionals use SNMP for monitoring and managing computer systems and the various components and
peripherals supported by their systems.
SNMP standards are defined by the Internet Engineering Task Force (IETF). SNMP version 1 was published in August 1988 and is the
most commonly supported version of SNMP. SNMP version 2 was first published in May 1993, but has not gained widespread market
acceptance. SNMP version 3 was recently completed and has addressed security issues that exist in version 1.
All SNMP systems consist of one or more managed systems that provide data through an SNMP agent to a management system. The
management system provides a user interface to view data from the managed systems. The management system and managed systems
communicate over a network (typically through User Datagram Protocol/Internet Protocol [UDP/IP]).
The management system and a managed system communicate by means of a common data schema. SNMP MIB files define the
structure, type, and values of the SNMP data. While MIBs can be standardized or enterprise specific, most operating systems supply
SNMP agents for the standard MIB-I and MIB-II schemas. MIB-I defines a base set of standard management information for systems
implementing the Internet Protocol (IP) suite. MIB-II defines characteristics of the system, characteristics of network interfaces, and
characteristics of components of the IP on the system. In addition to the standard MIBs, many hardware vendors have defined MIBs that
provide management data specific to their systems and peripheral devices.
Monitored data can be retrieved through SNMP using the Get command. Typically, this command requires the host name or IP address of
the target machine as well as the OID of the data to retrieve. Exact details are dependent on the operating system and the development
tools being used to create the management application. The Get command has a variant known as GetNext.
Management Information Base Object Identifiers
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 11. 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)
In the preceding example, the OID prefix for the Dell enterprise would be 1.3.6.1.4.1.674.
Introduction
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