Transcript Chapter 21

Network Management: SNMP
The roots of education are bitter, but
the fruit is sweet.
- Aristotle
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Objectives
• Describe the basic network management
architecture
• Explain the role that Simple Network Management
Protocol plays in an IP-based network
• Describe the 5 layers (or, components) of the OSI
Network Management model
• Explain the types of PDUs used by SNMP v3
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Network Management Architecture
• The basic network management architecture consists of a
set of devices being managed (known as managed devices
or agents), and a centralized management station (known
as a management entity or a manager)
• At each managed device, a piece of software called a
management agent collects data about the managed device
(e.g. received and sent traffic, errors, link utilization levels,
etc.) and stores them in a management database
• The management entity periodically requests (or, polls)
managed devices to send recent data about themselves.
Management agents in managed devices respond to these
requests by sending data stored in their database
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Network Management Architecture
•
Management entity acts as a repository for data
collected over time from managed devices. Using third
party software, these received data can be processed to
present information to network managers in various
forms (such as graphs) showing trends over time.
•
In addition to responding to periodical requests for data
from the management entity, managed devices may
report abnormal events on their own (called alerts or
traps)
1. When alerts are received, management entity generates
appropriate responses (such as operator notification,
event logging, system shutdown or restart, and other
kinds of automated attempts to repair affected systems)
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Network Management Architecture
• Management entities (Manager) and managed devices
(Agents) use SNMP - Simple Network Management
Protocol to communicate and exchange data
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OSI Network Management Model
• OSI network management model defines a common
frame of reference for network management, and
provides a framework for major functions that
network management systems perform
• The OSI network management model incorporates
the following five layers:
– Accounting management
– Configuration management
– Fault management
– Performance management
– Security management
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OSI Network Management Model
• Accounting management:
– focuses on using network and service utilization parameters
to assign usage charges back to various divisions within an
organization
• Configuration management:
– focuses on documenting network and system configuration
data about operating system or firmware, network interfaces,
protocols and related settings, etc.
– provides centralized access to and control over configuration
data
• Fault management:
– focuses on detecting, logging and repairing network and
system problems
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OSI Network Management Model
• Performance management:
– focuses on measuring and monitoring network traffic levels,
utilization, and other statistical metrics (such as throughput,
response times, error rates) to help maintain network and
system performance at acceptable levels
– helps identifying abnormal performance
• Security management:
– focuses on controlling access to network resources to avoid
various intrusions and attacks
– restricts access to resources based on proper authentication
and authorization
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Management Components
• SNMP: defines the format of messages exchanged
between a manager and an agent.
• SMI (Structure of Management Information): defines
general rules for:
– naming objects (“objects” are variables within the
management database that holds data)
– their types (including range and length)
– how to encode objects and their values
– SMI v1 - RFC 1155, SMI v2 - RFC 2578
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Management Components
• MIB (Management Information Base): creates a set
of named objects, their types, and their relationships
to each other in a managed device (such as a router),
similar to meta data in a database
• SMI requires that each object (such as:
udpInDatagrams) in a managed device have a
unique name.
• To name objects globally, SMI uses an object
identifier, which is a hierarchical identifier based on a
tree structure
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Figure 21.3
Management overview
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Figure 21.5
Object identifier
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Management Information Base (MIB)
• Currently, MIB-2 (RFC 1213) is the popular general
MIB supported by most SNMP-managed devices
• MIB-2 provides general TCP/IP management info
including interface statistics (interface speed, MTU
size, bytes sent, bytes received, etc.) and various
other things pertaining to the system itself (location,
contact, etc.)
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SNMP Messages
• SNMP managers and agents communicate over
UDP with a specific set of Protocol Data Units
• SNMP v3 defines 8 types of PDUs:
– GetRequest
– GetNextRequest
– GetBulkRequest
– SetRequest
– Response
– Trap
– InformRequest
– Report
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Figure 21.19
SNMP PDUs
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SNMP PDUs
• GetRequest: sent from a manager to the agent
to read the value of a variable (object) in the MIB
• GetNextRequest: mostly used by a manager to
get values of the entries in a MIB table
• GetBulkRequest: sent by a manager to retrieve
a large amount of data from an agent
• SetRequest: sent from a manager to the agent
to set (or, write) a value in a MIB variable
• Trap: sent from an agent to a manager
unsolicited to report an event
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SNMP PDUs
• Response: sent from an agent to a manager in
response to a GetRequest or GetNextRequest.
It contains value(s) of the variable(s) requested
by the manager
• InformRequest: sent from one manager to a
remote manager to get the value(s) of some
variable(s) from agents under the control of the
remote manager
• Report: to report errors between managers.
Not in use yet.
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