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Chapter 8: Network Management
Chapter goals:
 introduction to network management
 motivation
 major components
 Internet network management framework
 MIB: management information base
 SMI: data definition language
 SNMP: protocol for network management
 security and administration
 presentation services: ASN.1
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Areas of Network Mangement
 Performance management - to quantify, measure, report,




analyze, and control the performance of different network
components;
Fault management - to log, detect and respond to fault
conditions in the network;
Configuration management - to track which devices are on
the managed network and the hardware and software
configurations of these devices;
Accounting management- to specify, log, and control user
and device access to network resources;
Security management- to control access to network
resources according to some well-defined policy;
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What is network management?
 autonomous systems (aka “network”): 100s or 1000s
of interacting hw/sw components
 other complex systems requiring monitoring, control:
 jet airplane
 nuclear power plant
 others?
"Network management includes the 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."
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Infrastructure for network management
definitions:
managing entity
agent data
managing
data
entity
network
management
protocol
managed devices contain
managed device
managed objects whose
data is gathered into a
agent data
Management Information
Base (MIB)
managed device
agent data
agent data
managed device
managed device
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Network Management standards
OSI CMIP
 Common Management
Information Protocol
 designed 1980’s: the
unifying net
management standard
 too slowly
standardized
SNMP: Simple Network
Management Protocol
 Internet roots (SGMP)
 started simple
 deployed, adopted rapidly
 growth: size, complexity
 currently: SNMP V3
 de facto network
management standard
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SNMP overview: 4 key parts
 Management information base (MIB):

distributed information store of network
management data
 Structure of Management Information (SMI):
 data definition language for MIB objects
 SNMP protocol
 convey manager<->managed object info, commands
 security, administration capabilities
 major addition in SNMPv3
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SMI: data definition language
Purpose: syntax, semantics of
management data welldefined, unambiguous
 base data types:
 straightforward,

OBJECT-TYPE
data type, status,
semantics of managed
object
 MODULE-IDENTITY
 groups related objects
into MIB module

Basic Data Types
INTEGER
Integer32
Unsigned32
OCTET STRING
OBJECT IDENTIFIER
IPaddress
Counter32
Counter64
Guage32
Time Ticks
Opaque
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SNMP MIB
MIB module specified via SMI
MODULE-IDENTITY
(100 standardized MIBs, more vendor-specific)
MODULE
OBJECT TYPE:
OBJECT TYPE:OBJECT TYPE:
objects specified via SMI
OBJECT-TYPE construct
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SMI: Object, module examples
OBJECT-TYPE: ipInDelivers
ipInDelivers OBJECT TYPE
SYNTAX
Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
“The total number of input
datagrams successfully
delivered to IP userprotocols (including ICMP)”
::= { ip 9}
MODULE-IDENTITY: ipMIB
ipMIB MODULE-IDENTITY
LAST-UPDATED “941101000Z”
ORGANZATION “IETF SNMPv2
Working Group”
CONTACT-INFO
“ Keith McCloghrie
……”
DESCRIPTION
“The MIB module for managing IP
and ICMP implementations, but
excluding their management of
IP routes.”
REVISION “019331000Z”
………
::= {mib-2 48}
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MIB example: UDP module
Object ID
Name
Type
Comments
1.3.6.1.2.1.7.1
UDPInDatagrams Counter32 total # datagrams delivered
at this node
1.3.6.1.2.1.7.2
UDPNoPorts
Counter32 # underliverable datagrams
no app at portl
1.3.6.1.2.1.7.3
UDPInErrors
Counter32 # undeliverable datagrams
all other reasons
1.3.6.1.2.1.7.4
1.3.6.1.2.1.7.5
UDPOutDatagrams Counter32 # datagrams sent
udpTable
SEQUENCE one entry for each port
in use by app, gives port #
and IP address
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SNMP Naming
question: how to name every possible standard
object (protocol, data, more..) in every
possible network standard??
answer: ISO Object Identifier tree:
hierarchical naming of all objects
 each branchpoint has name, number

1.3.6.1.2.1.7.1
ISO
ISO-ident. Org.
US DoD
Internet
udpInDatagrams
UDP
MIB2
management
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OSI
Object
Identifier
Tree
Check out www.alvestrand.no/harald/objectid/top.html
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The presentation problem
Q: does perfect memory-to-memory copy
solve “the communication problem”?
A: not always!
struct {
char code;
int x;
} test;
test.x = 256;
test.code=‘a’
test.code
test.x
a
00000001
00000011
host 1 format
test.code
test.x
a
00000011
00000001
host 2 format
problem: different data format, storage conventions
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Solving the presentation problem
1. Translate local-host format to host-independent format
2. Transmit data in host-independent format
3. Translate host-independent format to remote-host
format
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ASN.1: Abstract Syntax Notation 1
 ISO standard X.680
used extensively in Internet
 like eating vegetables, knowing this “good for you”!

 defined data types, object constructors
 like SMI
 BER: Basic Encoding Rules
 specify how ASN.1-defined data objects to be
transmitted
 each transmitted object has Type, Length, Value
(TLV) encoding
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TLV Encoding
Idea: transmitted data is self-identifying
T: data type, one of ASN.1-defined types
 L: length of data in bytes
 V: value of data, encoded according to ASN.1
standard
Tag Value Type

1
2
3
4
5
6
9
Boolean
Integer
Bitstring
Octet string
Null
Object Identifier
Real
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TLV
encoding:
example
Value, 259
Length, 2 bytes
Type=2, integer
Value, 5 octets (chars)
Length, 5 bytes
Type=4, octet string
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Basic Concepts of SNMP
 An integrated collection of tools for network
monitoring and control.


Single operator interface
Minimal amount of separate equipment. Software and
network communications capability built into the existing
equipment
 SNMP key elements:
 Management station
 Managament agent
 Management information base
 Network Management protocol
• Get, Set and Notify
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SNMP protocol
Two ways to convey MIB info, commands:
managing
entity
request
response
agent data
Managed device
request/response mode
managing
entity
trap msg
agent data
Managed device
trap mode
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Protocol context of SNMP
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Proxy Configuration
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SNMP v1 and v2
 Trap – an unsolicited message (reporting an
alarm condition)
 SNMPv1 is ”connectionless” since it utilizes
UDP (rather than TCP) as the transport
layer protocol.
 SNMPv2 allows the use of TCP for
”reliable, connection-oriented” service.
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SNMP protocol: message types
Message type
GetRequest
GetNextRequest
GetBulkRequest
InformRequest
SetRequest
Response
Trap
Function
Mgr-to-agent: “get me data”
(instance,next in list, block)
Mgr-to-Mgr: here’s MIB value
Mgr-to-agent: set MIB value
Agent-to-mgr: value, response to
Request
Agent-to-mgr: inform manager
of exceptional event
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SNMP protocol: message formats
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Comparison of SNMPv1 and SNMPv2
SNMPv1 PDU
SNMPv2 PDU
Direction
Description
GetRequest
GetRequest
Manager to agent
Request value for
each listed object
GetNextRequest
GetNextRequest
Manager to agent
Request next value
for each listed object
------
GetBulkRequest
Manager to agent
Request multiple
values
SetRequest
SetRequest
Manager to agent
Set value for each
listed object
------
InformRequest
Manager to manager
Transmit unsolicited
information
GetResponse
Response
Agent to manager or
Manage to
manager(SNMPv2)
Respond to manager
request
Trap
SNMPv2-Trap
Agent to manager
Transmit unsolicited
information
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SNMPv1 Community Facility
 SNMP Community – Relationship between
an SNMP agent and SNMP managers.
 Three aspect of agent control:
Authentication service
 Access policy
 Proxy service

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SNMPv1 Administrative
Concepts
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SNMPv3
 SNMPv3 defines a security capability to be
used in conjunction with SNMPv1 or v2
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Traditional SNMP Manager
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SNMPv3 Flow
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SNMP3 Message Format with
USM
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User Security Model (USM)
 Designed to secure against:
 Modification of information
 Masquerade
 Message stream modification
 Disclosure
 Not intended to secure against:
 Denial of Service (DoS attack)
 Traffic analysis
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SNMP v.3 security and administration
 encryption: DES-encrypt SNMP message
 authentication: compute, send MAC(m,k):
compute hash (MAC) over message (m),
secret shared key (k)
 protection against playback: use nonce
 view-based access control
SNMP entity maintains database of access
rights, policies for various users
 database itself accessible as managed object!

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USM Timeliness Mechanisms
 USM includes a set of timeliness mechanisms to
guard against message delay and message replay.
 If a message is considered to be outside of the
time window, then the message is considered not
authentic, and an error indication is returned to
the calling module.
 Timeliness checking is done only if the
authentication service is in use and the message is
authentic, assuring the validity of the message
header fields.
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Key localization
 For the use of the authentication and privacy services it is





required that a secret authentication key and a secret
privacy key must be used for communications.
The keys can be generated from the user password using a
special algorithm.
A single password could be used to generate a single key for
both authentication and encryption.
A more secure scheme is to use two passwords and to
generate two different keys.
A localized key is a secret key shared between a user and
a remote SNMP engine.
The process by which a single user key is converted into
multiple unique keys is called key localization.
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Key Localization Process
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View-Based Access Control Model
(VACM)
 VACM has two characteristics:
Determines whether access to a managed
object should be allowed.
 Make use of an MIB that:

• Defines the access control policy for this agent.
• Makes it possible for remote configuration to be
used.
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Elements of the VACM Model
 Group – a set of <securityModel,
securityName> tuples on whose behalf
objects can be accessed
 MIB context - named subset of the object
instances in the local MIB
 MIB view – specific set of of managed
objects
 Access policy – particular set of access
rights (read, write, notify)
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Access determination depends on:
 Principal making the access request
 Security level requested
 Security model
 MIB context for the request
 Object instance for which access is
requested
 Type of access requested (read, write
notify)
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Access control processing
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Motivation for VACM
 In SNMPv1 the security related
information is lumped into a single variable
– community. By this flexibility and
functionality are lost.
 VACM provides the same set of security
related information using distinct variables
for each item.
 This is substantial improvement over
SNMPv1. It uncouples various concepts so
that values can be assigned to each one
separately.
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