TNM Lecture6

7/29/2019 TNM Lecture6

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Telecom Network Management

SNMPv1 Network Management:

Organization and Information Models

Sheeba Philips


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A Managed LAN and System Information acquired by an NMS

NMS on subnet 192.168.252.1 manages therouter and the hubs on subnet 172.16.46.1across the backbone network System Up Time in hundredths of a second


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Organization Model

Describes the components of an NMS and their functions

Agent, Manager, Object

Information Model

Describes the structure and organization of Management Information

SMI, MIB

Communication Model

Management Application processes in the Application Layer

Layer Management between Layers

Layer Operations within the Layers

Functional Model

FCAPS

Network Management Model - OSI


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The SNMP Model

Organization Model

Relationship between network element, agent, and manager

Hierarchical architecture

Information Model

Uses ASN.1 syntax

SMI (Structure of Management Information)

MIB ( Management Information Base) Communication Model

Transfer syntax

SNMP over TCP/IP

Communication services addressed by messages

Security framework community-based modelFunctional model is not explicitly addressed in SNMP. Security is covered as a

part of communication.


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The SNMP Organization Model: Two-Tier

Network Agent process residing in the managed object

Network Manager residing in the NMS managing the managed object Any host that could query an agent is a manager

Agent responds to any Mgmt system that talks to it using SNMP

Common practice:

Use an NMS to monitor a Network of multiple vendor NMS as an NMS provided by

the same vendor has more capabilities than other vendors NMS. Network Manager receives raw data from the agents and processes them.


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Useful when we want temporal data like, data traffic as a function of time

Instead of Manager polling, an intermediate agent is inserted between the agent and themanager.

RMON (Remote Monitoring) gathers data from MO, analyses the data, and stores the data

RMON acts as an agent and a manager; Communicates the statistics to the manager

The Manager receives data from the managed object as well as the intermediate agent

The SNMP Organization Model: Three-Tier


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Used when it is required to manage non-SNMP Managed objects using SNMP

Network elements do not have SNMP agents, eg. legacy systems management, wireless networks The information from these elements are gathered using associated tools

Proxy server at a central location converts the non-SNMP data into a set compatible with SNMP

Proxy server communicates with the SNMP Manager

Three -Tier Organization Model: Proxy Server


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Similar to Client-Server Architecture

While collecting data from Network elements, acts like a Manager

While providing data to another Network Manager, acts like an Agent

eg. two telecommunication service providers managing their respective WANs, but needing toexchange information to provide end-t-end services to the customers

NMS Behaving as Manager and Agent


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SNMP Network Management Architecture


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SNMP Architecture and Messages

Three goals of the Architecture of SNMP: Management functions on the Agent should be minimal and simple Should be flexible to allow expansions Should be independent of the architecture of any particular hosts or gateways

SNMP manages the network with 5 messages: 3 Messages from the Manager to the Agent, 2from the Agent to the Manager get-request: Sent by manager requesting data from agent

get-next-request: Sent by manager requesting data on the next MO to the one specified

set-request: Initializes or changes the value of network element

get-response: Agent responds with data for get and set requests from the manager

Trap - generic trap, specific trap, timestamp: Alarm generated by an agent

SNMP messages are exchanged using connectionless UDP protocol


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The SNMP Information ModelDescribes:

The structure and storage of management information (SMI defined in RFC1155)

The representation of objects and their relevant management information

The information base to describe the managed objects and their relationships(MIB defined in RFC 1213)

SMI (Structure of Management Information) defines the syntax and semantics of themanagement information stored in the MIB (Management Information Base)

Manager MIB Consists information of all the agent MIBs

Agent MIB Its own view

Objects by private vendors, if they conform to SMI defined by RFC 1155 and haveMIBs specified by RFC 1213, can be managed by SNMP-compatible NMS


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Structure of Management InformationManaged Object comprises of:

Object TypeDefines the Management Information: OID, Syntax used to

communicate, and Encoding Rules for the object

Object InstanceInstance of the objectMultiple instances of an object typeeg.Two similar routers from the same vendor. Multiple instances of this router in theNetwork

Object identifier (OID) is data type, not instance

Object instance IP address; Each IP address is an instance of the object

All Cisco routers of the same version have identical identifier; they are distinguishedby the IP address


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Every object type is uniquely identified by:

a DESCRIPTOR and

an OBJECT IDENTIFIER (OID)

eg. internet MIB has its OID: 1.3.6.1

internet OBJECT IDENTIFIER ::= {iso standard dod internet}

internet OBJECT IDENTIFIER ::= {1 3 6 1}

Any combination of the unique node number and unique name can be used

eg. internet OBJECT IDENTIFIER ::= {iso(1) standard dod(6)internet}

Any object in the internet MIB will start with the prefix 1.3.6.1 or internet

Object Type: Name


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Examples of OID

directory OBJECT IDENTIFIER ::= {internet 1}

mgmt OBJECT IDENTIFIER ::= {internet 2}

experimental OBJECT IDENTIFIER ::= {internet 3}

private OBJECT IDENTIFIER ::= {internet 4}

mgmt OBJECT IDENTIFIER ::= {1 3 6 1 2}


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Object Type: Syntax

ASN.1 Data Type syntax is used to define structure ofobject types (SMI) in SNMP Management.

Data Type - defined by its structure and tag Structure: Simple (Primitive),Defined (Application), Constructor (Structured) Tag: Class, Tag Number

Class: Universal

All built in data types Available in all applications

Application Application specific Can override Universal Tag Number

Context-specific Subset of an Application and limited to that

application Private

Used by Vendors of N/w products All the nodes under the vendor node will be

private tags


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Data type: Simple (Primitive)

Structure Data Type CommentsPrimitive types INTEGER Subtype INTEGER (n1..nN)

Special case: Enumerated

INTEGER type

OCTET STRING 8-bit bytes binary and textual data

Subtypes can be specified by

either range or fixedOBJECT IDENTIFIER Object position in MIB

NULL Placeholder


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Data Types: Defined Types

IpAddressDotted decimal IP AddressUsed to define IP Address of a Network element.Internallyit is an OCTET STRING of length 4

Counter

Wraparound non negative incrementing integer,Used for defining values which always increaseeg. Input packets received on an interface

Defined types NetworkAddress Not used

IpAddress Dotted decimal IP address

Counter Wrap-around, non-negative

integer, monotonically increasing,max 2^32 -1

Gauge Capped, non-negative integer,increase or decrease

TimeTicks Non-negative integer inhundredths of second units

Opaque Application-wide arbitrary ASN.1syntax, double wrapped OCTET

STRINGGaugeCapped non negative integer, increase or decreaseUsed for defining values which can increase or decreaseeg. No. of interfaces that are active on a hub

TimeTicks

Non negative integer in hundredths of second unitsTime measured in 100ths of a second from the time it was initialized

to 0 upto the current instant. eg. System Up time

Opaque Application wide arbitrary syntax.Used to create data types based on previously defined data types.


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Data Types: Constructor TypesSEQUENCE List Maker; Used to make a list of data types

SEQUENCE {, ,.,}

eg. List: IpAddrEntry::= SEQUENCE {ipAdEntAddr IpAddress

ipAdEntIfIndex INTEGERipAdEntNetMask IpAddress

ipAdEntBcastAddr INTEGER

ipAdEntReasmMaxSize INTEGER(0..65535)

}

SEQUENCE OF Table Maker; Makes a table from the listSEQUENCE OF

where list is a list made using SEQUENCE

eg Table: IpAddrTable ::= SEQUENCE OF IpAddrEntry

SET and SET OF are not used in SNMP


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Object Type: Encoding

SNMPv1 uses Basic Encoding Rules (BER) for encoding the information to be transmittedbetween the agent and the manager.

BER uses the tag length value (TLV) notation

The first octet of the encoding is the tag,

then the length of the value, then the value.

OID is encoded as an octet string.

IP Address is encoded as octet strings

Counter, gauge andTimeTicks are coded as integers

Opaque is octet string

Type Length Value

Class

(7-8th bits)

P/C

(6th bit)

Tag Number

(1-5th bits)

SNMP Data Types and Tags

Type Tag

OBJECT IDENTIFIER UNIVERSAL 6

SEQUENCE UNIVERSAL 16

IpAddress APPLICATION 0

Counter APPLICATION 1

Gauge APPLICATION 2

TimeTicks APPLICATION 3

Opaque APPLICATION 4


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Structure of Managed Objects

Managed Object has 5 parameters:

Textual nameIs mnemonic and starts with a small letter, eg. sysUpTime,sysDescr, etc. Also called OBJECT DESCRIPTOR

SyntaxIs the ASN.1 definition of the object, eg. OCTET STRING, INTEGERetc.

Definition - Textual description of the object

Access

Type of privilege associated with the object: eg. read-only, read-write ornot-accessible

Statusspecifies whether the object is current or obsolete. A managed objectonce defined can only be made obsolete and not removed or deleted. If it iscurrent, then specify whether its implementation is optional or mandatory

eg. sysDescr: {system 1}

Syntax: OCTET STRINGDefinition: A textual description of the entity

Access: read-only

Status: mandatory


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Aggregate Object

An aggregate object is a group of related objects

eg. IpAddrEntry::= SEQUENCE{

ipAdEntAddr IpAddress

ipAdEntIfIndex INTEGER

ipAdEntNetMask IpAddress

ipAdEntBcastAddr INTEGER

ipAdEntReamMaxSize INTEGER}

ipAddrTable::=SEQUENCE OF IpAddrEntry

ipAddrTable {ip 20}

Syntax SEQUENCE OF IPAddrEntryDefinition ..

Access not-accessible

Status mandatory


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Aggregate Object as Columnar Object


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ipAddrTable {internet 20} or {1.3.6.1.2.1.4.20}

ipAddrEntry (1)

ipAdEntAddr (1)ipAdEntIfIndex (2)

ipAdEntNetMask (3)

ipAdEntBcastAddr (4)

ipAdEntReamMaxSize (5)

OID of ipAdEntIfIndex is {1.3.6.1.2.1.4.20.1.2}

Row ipAdEntAddr ipAdEntIfIndex ipAdEntNetMask ipAdEntBcast

Addr

ipAdEntReasm

MaxSize

1 123.34.23.1 1 255.255.255.0 0 12000

2 123.34.23.2 3 255.255.255.0 0 12000

3 123.34.23.3 2 255.255.0.0 1 12000

ipAdEntAddr OID for Row 3 : {1.3.6.1.2.1.4.20.1.1.123.34.23.3}

ipAdEntBcastAddr OID for Row 2 :{1.3.6.1.2.1.4.20.1.4. 123.34.23.2 }

A Multiple-Instance Managed Object: ipAddrTableConsists of objects:

IP address

Interface Subnet mask (which subnet this address

belongs to)

Broadcast address (value of l.s.b. in IP

broadcast address)

Largest IP datagram that can be assembled


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Management Information Base

A MIB example: Internet MIB

Objects that are related are

grouped into groups


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System Group


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Interfaces Group

IfEntry OBJECT-TYPE

SYNTAX IfEntryACCESS not-accessible

STATUS mandatory

DESCRIPTION

"An interface entry containing

objects at the subnetwork layer and

below for a particular interface."

INDEX {ifIndex}

::= {ifTable 1}

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