Scalar And Tabular Objects - Juniper SECURITY THREAT RESPONSE MANAGER 2008.2 - SNMP AGENT GUIDE REV 1 Manual

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Table of Contents

Object Identifier with

Instance Indexes

Scalar and Tabular

Objects

Note that this example is a relative OID. An OID may combine both symbolic and

numeric representations of individual nodes of the OID tree, for example,

gmt.mib-2.1.sysDescr.

Absolute OID names must always begin with a dot and specify every node of the

OID tree from the top-most node to the specific managed object. For example:

.iso.org.dod.internet.mgmt.mib.system.sysDescr

.1.3.6.1.2.1.1.1

.iso.3.dod.1.mgmt.mib-2.1.sysDescr

To obtain values of objects from the manager, you must specify the instance of the

object. The instance of an object is specified by appending an instance index to the

object identifier. For example, the last 0 in: .iso.3.dod.1.mgmt.mib.1.sysUpTime.0

is the instance index. An instance index of 0 specifies the first instance and 1

specifies the second instance. Since sysUpTime is a scalar object, it has only one

instance. Therefore, an instance index of 0 is always specified when retrieving the

value of a scalar object. An instance index higher than 0 can only be used in the

case of columnar objects, which can have multiple instances.

A managed object has both a type (defined in ASN.1) and a value. For example,

the SNMP system group variable sysLocation (as defined in RFC1213-MIB ) has

the type, DisplayString may have the value STRM.

Managed objects, in SNMP, are of two types: scalar objects and tabular objects. A

managed object with a single instance is called a scalar object. Tabular objects

have multiple instances, such as the rows of a table. For example, the MIB II

system group has seven leaf variables included. Each of these objects is a scalar

object. For example, the value of sysUpTime is the duration of time since

re-initialization of the network management software (SNMP agent), measured in

hundredths of a second.

Tables in SNMP are two-dimensional objects defined as an ASN.1 type called

SEQUENCE OF, which allows 0 or more members. Each element of the sequence

is an entry (row) in the table, which is a sequence of scalar-valued objects. SNMP

does not allow tables to be nested within tables. For example, the MIB II at group

contains one tabular object, the atTable, which contains one row for each of a

system's physical interfaces. Each row in the table is an instance of the object

atEntry. Each row contains instances of the scalar-valued leaf objects atIfIndex,

atPhysAddress, and atNetAddress. The leaf objects are called columnar objects

since the instances of each such object constitute one column in the table.

Although these objects have scalar-valued instances, they are not scalar objects

because they can have multiple instances.

STRM SNMP Agent