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SNMP Agent MIB Reference

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SNMP MIB

The following sections define an SNMP-compliant MIB and introduce the SNMP MIB for BEA Tuxedo 9.1:

 

What Is an SNMP-Compliant MIB?

Each management station or agent in an SNMP-managed network maintains a local database of information relevant to network management, known as the management information base (MIB). The relationship between the management station, the agent, and the MIB is shown in the following figure.

Figure 1-1 SNMP-Managed Configuration

SNMP-Managed Configuration


 

An SNMP-compliant MIB contains definitions and information about the properties of managed resources and the services that the agents support. The manageable features of resources, as defined in an SNMP-compliant MIB, are called managed objects or management variables (or just objects or variables).

A management station gets and sets objects in the MIB, and an agent notifies the management station of significant but unsolicited events called traps. All message exchanges between the management station and its agents take place using the Simple Network Management Protocol (SNMP).

The MIB at the management station contains network management information extracted from the MIBs of all the managed entities in the network.

 

MIB Information Structure

The structure of management information (SMI), an SNMP standard described in the NWG RFC 1155, defines the structure of the MIB information and the allowable data types. The SMI identifies how resources within the MIB are represented and named. The philosophy behind SMI is to encourage simplicity and extensibility within the MIB.

The SNMP specification includes a template, known as an Abstract Syntax Notation One (ASN.1) OBJECT TYPE macro, which provides the formal model for defining objects and tables of objects in the MIB. The following keywords are used to define a MIB object:

Syntax

Defines the abstract data structure corresponding to the object type. The SMI purposely restricts the ASN.1 constructs that can be used to promote simplicity.

Access

Defines whether the object value may only be retrieved but not modified (read-only) or whether it may also be modified (read-write).

Description

Contains a textual definition of the object type. The definition provides all semantic definitions necessary for interpretation; it typically contains information of the sort that would be communicated in any ASN.1 commentary annotations associated with the object.

 

MIB Object Identifiers

Each object in the MIB has an object identifier (OID), which the management station uses to request the object's value from the agent. An OID is a sequence of integers that uniquely identifies a managed object by defining a path to that object through a tree-like structure called the OID tree or registration tree. When an SNMP agent needs to access a specific managed object, it traverses the OID tree to find the object. The MIB object identifier hierarchy and format is shown in the following figure.

Figure 1-2 SNMP MIB Object Identifier Hierarchy and Format

SNMP MIB Object Identifier Hierarchy and Format


 

In this hierarchy, each BEA private MIB object that the BEA SNMP Agent software manages has a unique object identifier. A prefix of .1.3.6.1.4.1.140 points to the objects in the BEA private MIB for the BEA SNMP Agent software.

Absolute and Relative Object Identifiers

Absolute OIDs specify a path to an attribute from the root of the OID tree. Absolute OID names always begin with a dot and must specify every node of the OID tree from the top-most node to the specific managed object. For example:

.1.3.6.1.2.1.1.1

Relative OIDs specify a path to the attribute relative to some node in the OID tree. For example, 2.1.1.1 specifies the sysDescr object in the system group, relative to the Internet node in the OID tree.

Specifying Object Identifiers

In addition to using the "dot-dot" notation, a series of integers separated by dots to describe OIDs, you can also express OIDs by using textual symbols instead of numbers to represent nodes in the path to the object, or by using a combination of both integers and textual symbols. A symbolic OID uses mnemonic keywords to specify the managed object. For example:

mgmt.mib-2.system.sysContact

The following numeric OID uses integers to specify the same managed object:

2.1.1.7

Note that 2.1.1.7 in this example is a relative OID.

An OID can combine both symbolic and numeric representations of individual nodes of the OID tree; for example:

mgmt.mib-2.1.sysContact

 

SNMP MIB for BEA Tuxedo 9.1

The SNMP MIB for BEA Tuxedo 9.1 is essentially an SNMP version of the Tuxedo management information base (TMIB) for BEA Tuxedo 9.1. The TMIB is the standard MIB for administering the components of a BEA Tuxedo or BEA WebLogic Enterprise application. For more information about the TMIB, see Understanding the Differences Between the SNMP MIB and the TMIB.

The SNMP MIB defines the data types and access permissions for the various managed objects that can be accessed through the BEA SNMP Agent software. It also defines the event notifications that can be generated by the BEA SNMP Agent software. As required by the SNMP standard, the SNMP MIB definitions are written in concise MIB format in accordance with RFC 1212.

BEA SNMP Agent provides a file named bea.asn1 for defining the SNMP MIB. For a BEA Tuxedo 9.1 installation, the bea.asn1 file resides in the tux_prod_dir/udataobj/snmp/etc directory, where tux_prod_dir represents the directory in which the BEA Tuxedo 9.1 distribution is installed.

The bea.asn1 file for BEA Tuxedo 9.1 makes the features of the following components recognizable and thus manageable within an SNMP network management framework:

You can use BEA SNMP Agent and the SNMP MIB for BEA Tuxedo 9.1 to manage Tuxedo 9.1, 9.0, 8.1, 8.0, 7.1, and 6.5 applications. You cannot use BEA SNMP Agent and the SNMP MIB for BEA Tuxedo 9.1 to manage WebLogic Enterprise 5.1 or earlier applications.

 

SNMP MIB Component MIBs

The SNMP MIB defined by the bea.asn1 file for BEA Tuxedo 9.1 refers to the entire database of management information at the management station or agent. The SNMP MIB, itself, consists of distinct component MIBs, each of which refers to a specific defined collection of management information that is part of the overall SNMP MIB. The management station uses the component MIBs to administer the particular components of the BEA Tuxedo system, to administer the agents themselves, and to collect information about the managed resources.

The SNMP MIB for BEA Tuxedo 9.1 consists of the following component MIBs:

With the exception of BEA Domain List, Traps, BEA System, and BEA Agent Integrator, the SNMP MIB component MIBs correspond to the TMIB component MIBs. For more information about the TMIB, see Understanding the Differences Between the SNMP MIB and the TMIB.

 

SNMP MIB Object Naming Conventions

The object names within the SNMP MIB for BEA Tuxedo 9.1 are prefixed with the letters tux. For example, the Core MIB contains a group named tuxTmachineTable, and the following objects are included within the tuxTmachineTable group:

tuxTmachinePmid

Represents a physical machine identifier

tuxTmachineLmid

Represents the logical machine identifier

 

SNMP MIB Object Definitions

The SNMP MIB definitions are written in concise MIB format in accordance with RFC 1212. Thus, the SNMP MIB stores only simple data types: scalars and two-dimensional arrays of scalars, called tables. Keywords SYNTAX, ACCESS, and DESCRIPTION as well as other keywords such as STATUS and INDEX are used to define the SNMP MIB managed objects.

To monitor or modify values of managed objects through your management station, you need to know which MIB objects represent the features of the BEA Tuxedo resources that are relevant to your management goals. You also need to know the data types, default values, and access permissions for these MIB objects.

For table objects, keep the following tips in mind:

 

SNMP MIB Event Trap Definitions

The bea.asn1 file defines a full range of BEA Tuxedo system and application events in accordance with RFC 1215, Trap definitions. These system and application events are transmitted as enterprise-specific traps to the management station. For a list of these traps, see Traps MIB.

The following keywords are used to define a trap:

ENTERPRISE

An object identifier that specifies the management enterprise under whose registration authority this trap is defined. All traps generated by the SNMP agent for BEA SNMP Agent have an enterprise field set to the following OID: .1.3.6.1.4.1.140.300. This value is passed in the enterprise field of the trap packet (Protocol Data Unit—PDU).

VARIABLES

Defines the ordered sequence of MIB objects that are contained in each instance of the trap type. Each variable is placed, in order, inside the variable-bindings field of the SNMP trap packet (PDU).

DESCRIPTION

Contains a textual definition of the trap type.

Trap ID

Specifies the enterprise-specific trap ID for the trap definition. The trap ID is passed in the specific trap ID field of the trap packet (PDU). The value of the generic trap ID field in traps is always set to 6, indicating an enterprise-specific trap.

 

Using the SNMP MIB

The management station uses the bea.asn1 file to set up the SNMP MIB for BEA SNMP Agent on the management station. The bea.asn1 file must be imported into the management database of the management station, as described in Using the BEA SNMP Agent with a Management Framework in BEA Tuxedo SNMP Agent Administration Guide.

The SNMP agent for BEA SNMP Agent uses a file named mib.txt to set up its local SNMP MIB on the managed node (machine). The mib.txt file, similar to the bea.asn1 file, provides a textual description of the content of the SNMP MIB. By default, the mib.txt file resides in the tux_prod_dir/udataobj/snmp/etc directory, where tux_prod_dir represents the directory in which the BEA Tuxedo 9.1 distribution is installed. For more information about using the mib.txt file to create the local SNMP MIB on a managed node, see BEA SNMP Agent Integrator Commands in BEA SNMP Tuxedo Agent Administration Guide.

The SNMP agent communicates with the TMIB of the managed BEA Tuxedo application to get the object values that initially populate the local SNMP MIB. As the management station gets and sets object values in the local SNMP MIB through the SNMP agent, the SNMP agent issues Tuxedo commands to read and write the comparable object values in the local TMIB.

The local SNMP MIB is not persistent, meaning that the SNMP MIB is not written to disk. When the SNMP agent process terminates, its SNMP MIB also terminates.

Querying Non-Existent MIB Objects

If you attempt to retrieve the value for an SNMP MIB object that does not exist, either no value is returned, or one of the following values is returned:

For example, if a BEA Tuxedo 8.0 or later application is not installed on the managed node, the CORBA-specific objects included in the SNMP MIB for BEA Tuxedo 9.1 do not return values when queried.

Updating MIB Objects

Some objects in the SNMP MIB can be set (updated) only under certain states of the BEA Tuxedo system. If you get an error while trying to set read-write objects in this MIB, examine the Tuxedo ULOG file for more information about the error.

The Tuxedo system creates a new ULOG file each day on each machine in a Tuxedo domain. For a description of the ULOG file, see reference page userlog(3c).

 

Understanding the Differences Between the SNMP MIB and the TMIB

The primary difference between the SNMP MIB for BEA SNMP Agent and the Tuxedo MIB (TMIB) is the use of terms. In addition, the SNMP MIB contains a few additional component MIBs.

The TMIB for a BEA Tuxedo system consists of distinct component MIBs, each used to administer a particular component of the Tuxedo system. These component MIBs are defined in individual reference pages each addressing the MIB for a particular part of the system. For example, reference page TM_MIB(5) in BEA Tuxedo File Formats, Data Descriptions, MIBs, and System Processes Referencedefines the MIB used to administer the fundamental aspects of a BEA Tuxedo 9.1 application. TM_MIB is comparable to the SNMP Core MIB.

Instead of referring to groups and managed objects, as is common in SNMP terminology, the TMIB defines application resources as classes and attributes. Classes are the administrative class definitions that make up the TMIB. Each class has a set of attributes that identifies individual items in the class. Examples of TMIB classes are:

T_MACHINE

The class definition for a machine

T_SERVICE

The class definition for Tuxedo services

Attributes for these classes are identified by the prefix TA_ followed by the attribute name. A few examples for the T_MACHINE class are:

TA_PMID

Represents a physical machine name

TA_LMID

Represents the logical machine name

For more information about the TMIB, refer to BEA Tuxedo File Formats, Data Descriptions, MIBs, and System Processes Reference.

 

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