SNMP Management Information

SNMP MANAGEMENT INFORMATION

• The foundation of  Network Management System is creation of database that  contains  information about the elements  to be managed. 

• An MIB is an structured collection of   information about objects   that are  part  of  the  network(servers, workstations, routers, bridges etc.)

• Each system in a network maintains a MIB that reflects the status of the managed resources at that system. NME (Network Management Entity) can monitor the resources at that system by reading the values of objects in the MIB and may control the resources at that system by modifying those values.

To serve these needs, the MIB must meet certain objectives:

•        Data base where manageable objects are defined.

•        The objects or objects used to represent a particular resources must be the same at each system. (Keeping data regarding active, passive or total open connections with any two of these data which must be uniform)

•        A common scheme for representation must be used to support interoperability.

The first points details the objects types and the second point details the type of structure for uniformity.

Structure Management Information

Structured Management Information explains ―How to write and define MIB‖. The SMI defines the general framework within which a MIB can be defined and constructed . The SMI identifies the data type that can be used in the MIB and specifies how within MIB are represented and named.

For the sake of simplicity, SMI must do the following:

•        Provide a standardized technique for defining the structure of a particular MIB

•        Provide standardized technique for defining individual objects, including the systems and the value of each object.

•        Provide a standardized technique for encoding object values.

MIB Structure

- The Internet Naming Hierarchy

- Objects Types

- Simple/Tabular Objects

-  Instances Identification

The Internet Naming Hierarchy

All managed objects in the SNMP environment are arranged in a hierarchical or tree structure. The leaf objects of the tree are the actual managed objects, each of which represents

some resources, activity or related information that is to be managed. The tree structure itself defines a grouping of objects into logically related sets. Each object is named by the sequence of the identifiers from the root to the object

The object identifier is : 1.2.4.12.3

Object Types:

A restricted subset of ASN.1 is used to describe objects types

Two ASN.1 classes are used :

Universal Types    Application Independent

Application-Wide Types  :

-  Defined in the context of a particular application

- Each application, including SNMP, is responsible for defining its own application-wide data types

Following data types are permitted :

Integer         (ex. : 5, -   10)

Octet string  (ex. : protocol)

Null             (object with no value associated)

Object identifier (ex. : 1.3.6.1.2)

And the constructor type (used to build tables) : Sequence, Sequence-          of

RFC 1155 defines the following application-wide     data types :

Network address ,                   IP address :       Internet 32- bit address

Counter : Non-  negative integer (can be incremented but not decremented)

Gauge : Non-      negative integer that may increase or decrease

Timeticks :          Non- negative integer counting the time in hundredths of second

Opaque : Arbitrary data transmitted in the form of an octet        string

Simpler And Tabular Objects

Simple Objects : Object with a unique  instance within the agent.

Its type is one of the following : integer, octet string,   null, object identifier,

network address, IP address, counter, gauge, time ticks or opaque.

Example: The ipInreceives object has one instance

Tabular Objects :

Two-dimensional table containing zero or more rows .

Each row is made of one or more simple objects ( components        ).

One or more components are used as indexes to unambiguously identifying the rows

The definition of tables is based on ASN.1 types ―Sequence" and "Sequence-  of "ASN.1 type.

• The table is indexed by ifIndex.

•Each row is an instance of the ifIndex,

ifPhysAddress and ifAdminStatus objects

The internet node has the object identifier value of 1.3.6.1. This value serves as the prefix for the nodes at the next lower level of the tree.

 The SMI document defines four nodes under the internet node: 

directory: reserved for future use with OSI directory

 mgmt : used for objects defined in IAB approved document. (Internet Activity Board) 

experimental : Used to identify objects used in internet experiments.

private : used to identify objects defined unilaterally.

The mgmt subtree consists of the definition of management information Bases that have been approved by the IAB (Internet Activity Board). At present two version of the MIB have been developed, mib -1 and mib-2. The second MIB is an extension of the first. Both are provided with the same object identifier in the subtree . Additional objects can be defined by

•        By expanding mib-2

•        By creating experimental mib

•        By creating private extensions under private tree structure.

MIB I defined 114 objects in 8 groups where as MIB II defined 173 objects with 10 groups.

Standard MIB’S:

MIB II object grouping is given above in the tree format: The only addition with respect to MIB I were addition transmission and snmp node objects as shown. MIB I was issued as RFC 1156 and the MIB II was defined in the RFC 1213. In this some additional object group are added. The mib II group is sub divided into the following groups.

•        system: overall information about the system.

•        interfaces:  information about each of the interfaces from the system to a sub network

•         at : address translation: description of address translation table for the internet to subnet address mapping

•         ip : information related to the implementation and execution experience of the IP on this system.

•         icmp: information related to the implementation and execution experience of ICMP on this system.

•         tcp: information related to the implementation and execution experience of UDP on this sytem.

•         egp: information related to the implementation and execution experience of EGP (External Gateway Protocol) on this system.

•         dot3 (transmission): information about the transmission schemes and access protocols at each system interface.

•         snmp: information related to the implementation and execution experience of SNMP on this system.