Snmp simple network management protocol based network management
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SNMP ( Simple Network Management Protocol ) based Network Management. Network Management: What is it?. Network management includes deployment,integration and coordination of the hardware, software, and human elements

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SNMP ( Simple Network Management Protocol ) based Network Management

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SNMP(Simple Network Management Protocol) based Network Management

NetworkManagement: What is it?

  • Network management includes

    • deployment,integration and coordination of the hardware, software, and human elements

    • to monitor, test, poll, configure, analyze, evaluate and control the network and element resources

    • to meet the real-time, operational performance, and Quality of service requirements at a reasonable cost.

Network Management: Why is it needed?

  • Lowers costs by eliminating the need for many administrators at multiple locations performing the same function

  • Makes network administration and monitoring easier and more convenient

  • Coherent presentation of data

Functional Areas of Network Management(According to OSI Network Management Model)

Performance Management– how smoothly is the network running

Fault Management- reactive and proactive network fault management (deals with problems and emergencies in the network)

Configuration Management– keeping track of device settings and how they function

Accounting Management- cost management and charge back assessment

Security Management- SNMP (Version 1 and 2) doesn’t provide much here

N/w Management arch.

Network Management Architectures

1) Management Entity job is to provide access to management data, controls, and behaviors:

  • Regular polling or sampling of management data

    • the management entity requests updates from managed devices to reflect recent status of the network being managed.

  • When alerts are received, appropriate responses must be generated

Network Management Architectures (contd.)

2) Managed Device

  • At each managed device, a special piece of software(process) called a management agent responds to polls for collected data,

  • The management agent itself has custody of a management database (MDB) of information that it collects and maintains over time

Network Management Architectures (contd.)

3) N/w Management Protocol

  • The protocol runs between managing entity and the managed device.

  • Allows the managing entity to query the status of the managed devices .

  • Agents can use the network management protocol to inform the managing entity of exceptional events.

SNMP & The OSI Model


  • Two major versions SNMPv1, SNMPv2

  • SNMPv1 is the recommended standard

  • SNMPv2 has become split into:

  • SNMPv2u - SNMPv2 with user-based security

  • SNMPv2* - SNMPv2 with user-based security and additional features

  • SNMPv2c - SNMPv2 without security

  • SNMPv3 - Security

Client Pull & Server Push

  • SNMP is a “client pull” model

The management system (client) “pulls” data from the agent (server).

  • SNMP is a “server push” model

The agent (server) “pushes” out a trap message to a (client) management system

The Internet- Standard Management Framework

  • SNMP is a tool (protocol) that allows for remote and local management of items on the network including servers, workstations, routers, switches and other managed devices.

  • Comprised of agents and managers

  • Agent - process running on each managed node collecting information about the device it is running on.

  • Manager - process running on a management workstation that requests information about devices on the network.

The Internet- Standard Management Framework (contd.)

SNMP network management consists of four parts:

  • Management Information Base (MIB)

  • A map of the hierarchical order of all managed objects and how they are accessed

  • Structure of Management Information (SMI)

  • Rules specifying the format used to define objects managed on the network that the SNMP protocol accesses

  • SNMP Protocol

  • Defines format of messages exchanged by management systems and agents.

  • Specifies the Get, GetNext, Set, and Trap operations

  • Security and administration capabilities

  • The addition of these capabilities represents the major enhancement in SNMPv3 over SNMPv2

Registered Tree


MIB-II Standard Internet MIB

  • Definition follows structure given in SMI

  • MIB-II (RFC 1213) is current standard definition of the virtual file store for SNMP manageable objects

  • Has 10 basic groups

    • system

    • interfaces

    • at

    • ip

    • icmp

    • tcp

    • udp

    • egp

    • transmission

    • snmp

  • If agent implements any group then is has to implement all of the managed objects within that group

Ports & UDP

  • SNMP uses User Datagram Protocol (UDP) as the transport mechanism for SNMP messages


IP Packet

SNMP Message


UDP Datagram

  • Like FTP, SNMP uses two well-known ports to operate:

  • UDP Port 161 - SNMP Messages

  • UDP Port 162 - SNMP Trap Messages

Four Basic Operations

  • Get

Retrieves the value of a MIB variable stored on the agent machine

(integer, string, or address of another MIB variable)

  • GetNext

Retrieves the next value of the next lexical MIB variable

  • Set

Changes the value of a MIB variable

  • Trap

An unsolicited notification sent by an agent to a management application (typically a notification of something unexpected, like an error)

Basic operations contd..



port 161


port 161





port 161



port 162

port 161


  • Traps are unrequested event reports that are sent to a management system by an SNMP agent process

  • When a trappable event occurs, a trap message is generated by the agent and is sent to a trap destination (a specific, configured network address)

  • Many events can be configured to signal a trap, like a network cable fault, failing NIC or Hard Drive, a “General Protection Fault”, or a power supply failure

  • Traps can also be throttled -- You can limit the number of traps sent per second from the agent

  • Traps have a priority associated with them -- Critical, Major, Minor, Warning, Marginal, Informational, Normal, Unknown

Trap Receivers

  • Management applications can handle the trap in a few ways:

  • Poll the agent that sent the trap for more information about the event, and the status of the rest of the machine.

  • Log the reception of the trap.

  • Completely ignore the trap.

Languages of SNMP

  • Structure of Management Information (SMI)

specifies the format used for defining managed objects that are accessed via the SNMP protocol

  • Abstract Syntax Notation One (ASN.1)

used to define the format of SNMP messages and managed objects (MIB modules) using an unambiguous data description format

  • Basic Encoding Rules (BER)

used to encode the SNMP messages into a format suitable for transmission across a network


  • The description of MIBs and message formats is based on the ASN.1 syntax.

  • The mapping from an abstract syntax upon a transfer syntax is defined by BER.

Basic Message Format

Message Length

Message Version

Message Preamble

Community String

PDU Header

SNMP Protocol Data Unit

PDU Body

  • Monolithic Agents

  • not extendible

  • optimized for specific hardware platform and OS

SNMP Agents

Two basic designs of agents

  • Extendible Agents

  • Open, modular design allows for adaptations to new management data and operational requirements

Community Names

  • A community string is a password that allows access to a network device. It defines what "community of people" can access the SNMP information that is on the device.

  • Community names are used to define where an SNMP message is destined for.

  • Set up your agents to belong to certain communities.

  • Set up your management applications to monitor and receive traps from certain community names.

  • There are actually three community strings for SNMP-speaking devices:

    • The SNMP Read-only community string

    • The SNMP Read-Write community string

    • The SNMP Trap community string

Proxy Management

  • A node may not support SNMP, but may be manageable by SNMP through a proxy agent running on another machine.

  • Nowadays the term proxy denotes a device that forwards SNMP messages, but doesn’t look at the individual objects.

Advantages of using SNMP

  • Standardized

  • universally supported

  • extendible

  • portable

  • allows distributed management access

  • lightweight protocol

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