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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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Structure of Managed Objects
SNMP:
Characteristics Values
Object Type OID
Syntax INTEGER | SEQUENCE | IpAddress |SEQUENCE OF |
Access Read-only | write-only | not-accessible
| read-write
Status Mandatory | optional | obsolete
Description text
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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}