ch05 snmp management information (old)

7/27/2019 Ch05 SNMP Management Information (Old)

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Chapter 5

SNMP Management

InformationChuChuChuChu----Sing YangSing YangSing YangSing Yang

Department of Electrical EngineeringDepartment of Electrical EngineeringDepartment of Electrical EngineeringDepartment of Electrical Engineering

National Cheng Kung UniversityNational Cheng Kung UniversityNational Cheng Kung UniversityNational Cheng Kung University


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Outline

Introduction Structure of Management Information

Practical Issues Summary


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Introduction

The foundation of a TCP/IP-based NMS is a

database containing information about the

elements to be managed

Referred as Management Information Base (MIB) Each resource to be managed represented by an object

Is a structured collection of objects

Is a database structure in the form of tree (for SNMP) Reflects the status of the managed resources at the system

Workstation, server, router, bridge, etc.)


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Objectives of the MIB

The object or objects used to represent a particularresource must be the same at each system

Defines the objects and the structuring of objects in MIB

Information stored the TCP entity at a system# of active opens, # of passive opens, total # of opens

MIB specifies the active and the passive open counts

A common scheme for representation must be used to

support interoperability

Defines a structure of management information (SMI)

Some of the practical issues involved in managing by means

of managed objects


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Outline


Practical Issues Summary


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Structure of ManagementInformation (SMI)

Specified in RFC 1155

Defines the general framework within which a MIB can be definedand constructed

Identifies the data types that can be used in MIB

Specifies how resources within the MIB are represented andnamed

Encourage simplicity and extensibility within the MIB

Does not support the creation or retrieval of complex data

structuresOSI management provides for complex data structures and retrieval models

to support greater functionality

Simplify the task of implementation

Enhance interoperability


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Structure of ManagementInformation (cont.)

MIB can store only simple data typesScalars and two-dimensional arrays of scalars

SNMP can retrieve only scalars

SMI must tightly restrict the definition of the

vender-created data types to avoid suffering

interoperability


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Structure of ManagementInformation (cont.)

SMI provides a standardized way of representingmanagement information

Provide a standardized technique for defining the

structure of a particular MIBProvide a standardized technique for defining

individual objects

The syntax and value of each object

Provide a standardized technique for encoding object

values


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MIB Structure

All managed objects in the SNMP environmentare arranged in a hierarchical or tree structure

The leaf objects are the actual managed objects

Represents resource, activity, or related information that isto be managed

Tree structure defines a grouping of objects into

logically related sets


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MIB Structure (cont.)

Abstract Syntax Notation One (ASN.1)Defined abstract syntax of application data

Defined the structure of application and presentation

PDUsDefined the MIB for both SNMP and OSI

Object Identifier

Serves to name the object

Is a unique identifier for a particular object type Its value consists of a sequence of integers


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MIB-II Object Groups


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Object Syntax

Every object is defined in a formal waydata type of the object,

its allowable forms,

value ranges

Its relationship to other objects within the MIB

ASN.1 notationDefines each individual object

Defines the entire MIB structure


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Object Syntax Universal Types

Consist of application-independent data types Data types in the Universal class

primitive types

Basic building blocks of other types of objects

integer, octetstring, null, object identifier

sequence, sequence of


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Object Syntax

Application-Wide Types

The APPLICATION class of ASN.1 consists of datatypes that are relevant to a particular application

RFC 1155 lists a number of application-wide datatypes networkaddress: the only defined address is IpAddress

Ipaddress: 32-bit address

counter: from 0 to 232-1 (4,294,967,295)

gauge: from 0 to 232-1

timeticks: the time in hundredth of a sec since some epoch

opaque: pass arbitrary data, may be in any format


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CounterMay be incremented, but not decremented

May wrap around

GaugeMay increase or decrease

Remain latched at the maximum until reset

Be used to Measure the current value of some entity

Store the difference in the value of some entity in a time interval

Monitor the rate of change of the value of an entity

Counter and Gauge


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Counter and Gauge (cont.)


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Counter and Gauge (cont.)

Latch counterSticks at the maximum value and must be reset

Problems

one management system only

multiple management systems

If the represented value falls below the gauge max

Allow the gauge to decrease

Leave the gauge stuck at its maximum value until reset


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Defining Objects

ASN.1 includesPredefined universal types

A grammar for defining new types that are derived

from existing types

MIB supports 2-D tables, or arrays of value

The macro used to defined SNMP MIBRFC 1155: MIB-I

RFC 1212: MIB-II


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Defining Objects (cont.)

Levels of definitionMacro definition

Defines the legal macro instances

Specifies the syntax of a set of related typesMacro instance

Specifies a particular type

Supplies arguments for parameters in the macrodefinition

Macro instance value Represents a specific entity with a specific value


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Example of an Object Definition

tcpMaxConn OBJECT-TYPE

SYNTAX INTEGER

ACCESS read-only

STATUS mandatory

DESCRIPTION

The limit on the total number of TCP connections

the entity can support. In entities where the

maximum number of connections is dynamic, this

object should contain the value -1.

={ tcp 4}


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Defining Tables

SMI supports only one form of structuring of data a simple 2-D table with scalar-valued entries

Definition of tables involves Sequence and sequence of ASN.1 type

indexPart of the OBJECT-TYPE macro

TCP connection table (tcpConnTable) Has the object identifier 1.3.6.1.2.1.6.13

The object contains information about TCP connectionmaintained by the corresponding managed entity

Each entry represents the state information for one connection

State information consists of 22 items for each conn.

Only 5 items are visible to network management


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Defining Tables (cont.)

SEQUENCE OFTcpConnEntry

ASN.1 constructs SEQUENCE OFconsists of one or moreelements, all of the same type

Each element is a row of the table

A table consists of zero or more rows

SEQUENCE

ASN.1 constructs SEQUENCEconsists of a fixed no. of

elements, possibly of more than one type Each row of the table contains elements of type

INTEGER, IpAddress, INTEGER (..65535), IpAddress, INTEGER(..65535)


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Defining Tables (cont.) INDEX

Determines which values will be used to distinguish one row inthe table

The four elements in the row used to distinguish a single row

from the table SMI does NOT permit nesting

Is not allow to define an element of a table to be another table

Encoding Objects in MIB are encoded using Basic Encoding Rules (BER)

associated with ASN.1

BER is a widely used, standardized encoding scheme


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MIB-II Specification on TCP Connection Table

MIB II S ifi ti TCP C ti T bl


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MIB-II Specification on TCP Connection Table


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Instance of a TCP Connection Table


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Outline


Practical Issues

Summary


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Practical IssuesMeasurement

Test environment for bridgesBridge

Network management station

LAN analyzer

Test stream

100 packets are generated by LAN analyzer 88 normal unicast packets (64~1500 octets)

12 packets with intentional frame check sequence

errors


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Practical Issues-Measurement

The test stream consists of 245 packets 120 packets contained IP datagrams with unicast MAC

address of the router 40 contained the routers IP address

45 contained a distant IP address with TTL=0 5 contained an invalid IP address

30 contained a valid IP address and a nonzero TTL

65 packets contained a broadcast MAC address and to be

delivered to a higher layer within the router 25 packets had an invalid protocol type in Ethernet header

35 packets had an incorrect framce check sequence


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Interface Group


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IP Group


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Practical Issues-Private MIBs

Interoperability should extend to private extensionsto the MIB

The management station must be loaded with theprivate MIB structure (with a formal description) Reads a MIB file from disk

Compiles it into the mgmt stations library of managedobjects

Three formats to define private MIBs The original SNMP SMI specification, RFC-1155

The newer Concise MIB Format, RFC-1212

The OSI SMI specification


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Practical Issues

Limitations of MIB Objects

A network management system is limited byCapabilities of the network management protocol

Objects used to represent the environment to be

managedA fine-grained set of MIB objects allows for

greater control of the network by paying the

costs Increased storage and processing at the agents

Increased SNMP traffic over the network


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Outline


Practical Issues

Summary


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Summary

SNMP frameworkManagement information is represented using

Abstract Syntax Notation One (ASN.1)

Management information base (MIB) Consists of a collection of objects organized into groups

Objects hold value that represent managed resources

Structure of management information (SMI) Defines the allowable ASN.1 types

Defines the allowable MIB structures

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