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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
Introduction Structure of Management Information
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
Introduction Structure of Management Information
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
Introduction Structure of Management Information
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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