Reference Guide

Table Of Contents
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 13. 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)
16 Introduction