Connectivity Guide

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)
EXPERIMENTA
L(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.
The numbers in boldface type show the categories and numbers that apply to Server Administrator. All Server Administrator-defined
OIDs consist of 1.3.6.1.4.1.674 followed by additional component values.
SNMP Security
SNMP version 1 has a very limited security mechanism. SNMP agents support the use of a community string, which is configured at
each SNMP agent and is passed as a part of all SNMP request messages. There is no verification that the requester is actually a
member of the specified community. As most system and network management data is not confidential, this limited security is
acceptable for Get types of requests. On the other hand, this security is not acceptable for Set types of operations where an SNMP
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