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INFO 331
Computer Networking
Technology II
Chapter 9
Network Management
Dr. Jennifer Booker
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Network Management History
• Network management didn’t exist in its
current form until the 1980’s
– From the ’40s to ’70s, networks were typically
very homogeneous (proprietary-only), so
network management tools were specific to
that insular environment, if used at all
– The advent of the PC and Macintosh made
networks get much more heterogeneous, and
increased the complexity of network
management
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Network Management
• A network typically consists of many unrelated
types of equipment, which are
all supposed to work together in perfect
harmony, in spite of the myriad protocols,
operating systems, interfaces, etc. involved
–
–
–
–
Servers and workstations
Routers, switches, and hubs
Wireless access points and hosts
Firewalls
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Network Management
• In order to manage this mess, there is
often a Network Operations Center (NOC)
to coordinate maintenance, upgrades,
monitoring, optimization (if you have time),
repairs, etc.
– Akin to a pilot’s cockpit, or the control room
for a power station, or the mixing board at
a concert
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Network Management
• We need to know
– What to monitor
• What is worth focusing your attention on?
– How to analyze what we see
– How to respond to changing conditions
(fix problems)
– How to proactively manage the system
(prevent problems)
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Typical Problems
• Even a simple network can have
challenges which help motivate the
need for network management
• Detect interface card failure at a host
or router
– The host or router might report the
interface failure to the NOC
– Better, network monitoring might reveal
imminent failure, so the card is replaced
before failure
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Typical Problems
• Monitor traffic to guide resource
deployment
– Traffic patterns or congestion monitoring
can show which parts of the network are
most used
– This could lead to improved usage of servers,
simplifying physical layout or improving the
speed of high traffic LAN segments, or make
good upgrade decisions
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Typical Problems
• Detect rapid routing changes
– Routing can become unstable, causing rapid
changes in routing tables (route flapping)
– The network admin would like to know this
is happening before something crashes as
a result!
• Host is down
– Network monitoring could detect a system
down before the user notices it
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Typical Problems
• Monitor SLAs
Not this SLA!
– Service Level Agreements (SLAs) are
contracts to guarantee specific services, such
as Internet service, in terms of availability,
throughput, latency, and other agreed-upon
measures
• Major ISPs (tier 1) can provide SLAs to major
business customers
– If you pay for this service, it’s nice to know if
they are really providing what you paid for!
Image from www.answers.com/topic/symbionese-liberation-army
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Typical Problems
• Intrusion detection
– The network admin can look for traffic from
odd sources, destined for unusual ports, lots
of SYN packets, and other security threats we
recently covered
– This can lead to refinement of filters &
firewalls
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ISO Network Management
• ISO has produced guidance on the types
of network management activities
– ISO network management (ISO/IEC
10733:1998)
– ISO security management (ISO/IEC TR
13335:2004, ISO/IEC 18026:2009 and
ISO/IEC 18028-1:2006)
• See Global IHS for buying ISO standards
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ISO Network Management
• Cisco overview white paper (free, unlike
ISO standards, and summarized herein thru
slide 35)
• ISO identifies five areas of network
management
– Fault, configuration, performance, security,
and accounting management
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ISO Network Management
• Fault Management
– Detect, isolate, notify, and correct faults
encountered in the network
• Configuration Management
– Configuration aspects of network devices
such as configuration file management,
inventory management, and software
management
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ISO Network Management
• Performance Management
– Monitor and measure various aspects of
performance so that overall performance
can be maintained at an acceptable level
• Security Management
– Provide access to network devices and
corporate resources to authorized individuals
• Accounting Management
– Usage information of network resources
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Fault Management
• This is the main focus of network
management for most organizations
• Faults are errors or problems in the
network
– Often a shorter term perspective than
performance management
• Hence fast detection of problems is
critical, often via color-coded graphical
network maps
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Fault Management
• Typically want a network management
platform to do:
– Network discovery and topology mapping
– Event handler
– Performance data collection and presentation
– Management data browsing
• Network management platforms include
HP OpenView, Aprisma Spectrum, and
Sun Solstice
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Fault Management
• Devices can send SNMP traps (RFC
3410) of events which change their status
• These events are logged, such as in a
Management Information Base (MIB)
• Platforms can be geographically located,
and communicate with each other to
centralize network monitoring
– Web interfaces on devices can allow remote
management and configuration
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Fault Management
• Equipment vendors often use different
management systems
– They can communicate using CORBA or CIM
standards to exchange management data
• Troubleshooting a network often uses
TFTP and syslog servers
– The trivial FTP (TFTP) server stores
configuration files; routers and switches can
send system log (syslog) messages to the
syslog server
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Fault Management
• Faults can be detected with SNMP trap
events, SNMP polling, remote monitoring
(RMON, RFC 2819) and syslog messages
– Module changing to up or down state
– Chassis alarms for hardware failures (fans,
memory, voltage levels, temperature, etc.)
– Responses can be just notification and
logging of the event, or shutdown of that
device, e.g. temps can be defined for warning,
critical, or shutdown
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Fault Management
• Fault detection can also be done at the
protocol or interface levels
– Such as a router interface failure
• A management station polls the device to
determine status or measure something
(CPU usage, buffer failure, I/O drops,
etc.), and flags it with an RMON alarm
when the measure exceeds some
threshold value
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Configuration Management
• Configuration management (CM) tracks
equipment and software in the network
• Can assess which elements are causing
trouble, or which vendors are preferred
– What if a vendor recalls a certain device?
Do you have any of them? Where?
– Whose routers or switches are most reliable?
– Where do you send a service vendor to
replace a dead router?
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Configuration Management
• CM data includes
– Make, model, version, serial number of equipment
– Software versions and licenses
– Physical location of hardware
• Site, building, room, rack number, etc.
– Contact info for equipment owners and
service vendors
• Naming conventions are often used to keep
names meaningful, not just yoda.drexel.edu
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Configuration Management
• CM also includes file management
– Changes to device configuration files should
be carefully controlled, so that older versions
can be used if the new ones don’t work
– A change audit log can help track changes,
and who made them
• Inventory management is based on the
ability to discover what devices exist, and
their configuration information
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Configuration Management
• Software management can include the
automation of software upgrades across
devices
– Download new software images, verify
compatibility with hardware, back up existing
software, then load new software
– Large sites may script the process and run
during low activity times
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Performance Management
• The same SNMP methods to capture fault
data can be used for performance data,
such as queue drops, ignored packets,
etc.
– These can be used to assess SLA
compliance
• On a larger scale, WAN protocols (frame
relay, ATM, ISDN) can also collect
performance data
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Performance Management
• Performance management tools include
– Concord Network Health
– InfoVista VistaView
– SAS IT Service Vision
– Trinagy TREND
• These all collect, store, and analyze data
from around one’s enterprise, and typically
use web-based interfaces to allow access
to it from anywhere
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Performance Management
• Increased network traffic has led to more
attention to user and application traffic
– RFC 4502 (replacing RFCs 2021 and 3273)
defines how RMON can be used to analyze
applications and the network layer, not just
lower layer (e.g. MAC) protocols
– Many other performance monitoring tools
exist, e.g. Cisco NetFlow
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Security Management
• Security management covers controlling
access to the network and its resources
– Can include monitoring user login, refusing
access to failed login attempts, as well as
either intentional or unintentional sabotage
• Security management starts with good
policies and procedures
– The minimum security settings for routers,
switches, and hosts is important to define
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Security Management
• Methods for control of security at the
device level (router) include
– Access control lists (ACLs) and what they
are permitted to do
– User ID’s and passwords
– Terminal Access Controller Access Control
System (TACACS)
• TACACS (RFC 1492) is a security protocol
between devices and a TACACS server
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Security Management
• A refinement of TACACS is TACACS+,
which gives more detailed control over
who can access a given device
– It separates the Authentication (verify user),
Authorization (control remote access to
device), and Accounting functions (collect
security information for network management)
(AAA)
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Security Management
• In Cisco’s world, AAA functions are
managed with commands such as
–
–
–
–
–
aaa
tacacs-server
set authentication
set authorization
set accounting
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Security Management
• In SNMP, configuration changes can be
made to routers and switches just like from
a command line
– Hence strong SNMP passwords are critical!
– SNMP management hosts (‘managing
entities’ in Kurose) should have static IP, and
sole SNMP rights with network devices
(managed devices) according to a specific
Access Control List (ACL)
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Security Management
• SNMP can set router security:
– Privilege Level = RO (read only) or = RW
(read and write); only RW can change router
settings
– Access Control List (ACL) can be set to only
allow specific hosts to request router
management info; ACL control over interfaces
can help prevent spoofing
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Security Management
– View – controls what router data can be
viewed
– SNMPv3 provides secure exchange of data
• Switches can restrict Telnet and SNMP via
an IP Permit List
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Accounting Management
• Accounting management measures
utilization of the network so that specific
groups or users can be billed correctly for
snarfing up resources
– Yes, it’s all about money
– Data can be collected using various tools,
such as NetFlow, IP Accounting, Evident
Software
• This can also be used to measure how
well SLAs are being followed or not
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Other aspects of net mgmt
• So network management is a huge field
• We’ll focus on basic infrastructure issues
– Omit service management, network
administration, provisioning, and sizing
networks (see TINA and TMN standards)
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Network Management
Infrastructure
• Network management is like the CEO of
an organization getting status reports from
middle managers, and they get status from
first line managers
– The CEO has to make decisions about the
entire company based on this data
• Corrective action may be needed, based on good
or bad results obtained
• The CEO of General Motors may build new plants,
or shut others down
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Network Management
Infrastructure
• Network management establishes managers
(called managing entities, often located in a
NOC) who are allowed (via an ACL) to talk to
network devices (managed devices, such as
servers or routers)
– Each managed device has a network management
agent, who collects the desired data
– Each managed device has one or more managed
objects (such as network cards, memory chips, etc.)
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Network Management Infrastructure
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Network Management
Infrastructure
• Descriptions of all managed objects, and
the devices they belong to, are collected in
the Management Information Base (MIB)
– A MIB is a database of managed object data
• Managed devices communicate with
managing entities using a network
management protocol
– Devices don’t generally talk to each other,
but managing entities can
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Network Management
Infrastructure
• The network
management
protocol doesn’t To
managing
manage the
entity
network per se –
it just provides a
means for the
network admin to
do so
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Managed device (host, server,
router, printer, etc.)
Network
mgmt Agent
Managed
object 1
Managed
object 2
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Network Management
Standards
• The architecture just described applies to
most any network management approach
• Many specific standards have been
developed
– The OSI CMISE/CMIP standards, used in
telecommunications
– In the Internet, SNMP (Simple Network
Management Protocol, RFCs 3411-3418)
• We’ll focus on SNMP
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SNMP isn’t Simple!
• Derived from SGMP (RFC 1028, 1987)
• Key goals of network management include
– What is being monitored?
– What form of control does the network
administrator have?
– What is the form of data reported and
exchanged?
– What is the communication protocol for the
exchange of data?
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SNMP
• To address these goals, SNMP has four
modular parts
– Network management objects, called MIB
objects
• The MIB tracks MIB objects
• A MIB object might be a kind of data (datagrams
discarded, description of a router, status of an
object, routing path to a destination, etc.)
• MIB objects can be grouped into MIB modules
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SNMP
– A data definition language, SMI (Structure of
Management Information)
• SMI defines what an object is, what data types
exist, and rules for writing and changing
management information
– A protocol, SNMP, for the exchange of
information and commands between
manager-agent and manager-manager
(between two managing entities)
– Security and administrative capabilities
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SMI
• SMI is defined by RFCs
2578-2580 (1999)
• SMI has three levels of
structure
– Base data types
– Managed objects
– Managed modules
SMI Modules
SMI Objects
SMI Base Data Types
[SMI is part of MIB, so a SMI object is
the same as a MIB managed object.]
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SMI
• SMI Base Data Types are an extension on the
ASN.1 structure (Abstract Syntax Notation One,
ISO/IEC 8824:2008)
• There are eleven basic data types (p. 767)
– Signed and unsigned (>0) integers, IP addresses,
counters, time in 1/100 second counts, etc.
– Most important is the OBJECT IDENTIFIER type,
which allows definition of an SMI object as some
ordered collection of other data types
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SMI
– The OBJECT IDENTIFIER is like a struct in C
– Here, it names an Object
• To create a managed object, the OBJECTTYPE construct is used
– Over 10,000 object-types have been defined
– these are the heart of data that can be
collected for network management
– Analogy: OBJECT IDENTIFIER defines the
class, OBJECT-TYPE instantiates the object
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SMI Objects
• An object-type includes four fields
– SYNTAX – is the data type of the object, e.g.
‘Counter32’
– MAX-ACCESS – is whether the object can be
read, written, created, e.g. ‘read-only’
– STATUS – is whether the object is current,
obsolete, or deprecated, e.g. ‘current’
– DESCRIPTION – gives a definition of the
object, which is a long text narrative
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SMI Modules
• The MODULE-IDENTITY construct
creates a module from related objects
– Fields include when it was last updated, the
organization who did so, contact info for them,
a description of the module, a revision entry,
and description of the revision
• The end of the MODULE-IDENTITY gives
the ASN.1 code for the type of information
in the module (often MIB-2)
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SMI Modules
• For examples, these MIB modules
(MODULE-IDENTITY) are defined
– For IP and ICMP in RFC 4293
– For TCP in RFC 4022
– For UDP in RFC 4133
– For RMON (remote monitoring) in RFC 4502
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SMI Modules
• There are other kinds of modules
– NOTIFICATION-TYPE for making SNMP-Trap
and information request messages
– MODULE-COMPLIANCE for defining
managed objects that an agent must
implement
– AGENT-CAPABILITIES defines what agents
can do with respect to object and event
notification definitions
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MIB
• The Management Information Base (MIB)
stores a current description of the network
• Data is collected from agents in each
device about the objects in that device
• There are over 200 standard MIB
modules, plus many more vendor-defined
• To identify these modules, the IETF
borrowed a convention from ISO – the
ASN.1 structure
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MIB
• The ASN.1 object identifier tree structure gives a
number (e.g. 1.3.6.1.2.45) to every object within
ISO, ITU-T, or joint ISO/ITU-T control
• We care about stuff under 1.3.6.1.2.1
– ISO (1)
• ISO identified organization (3)
– US DoD (6)
» Internet (1)
»
Management (2)
»
MIB-2 (1)
(ran out of indents!)
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MIB
• Under the MIB-2 category, we have 16
choices, including
– System (1)
– Interface (2)
– Address translation (3)
– Lots of protocols (ip, icmp, tcp, udp, etc.)
– Transmission (10)
– SNMP (11)
– RMON (16)
Apologies to http://www.sptimes.com/2002/07/08/Xpress/Letdown_aside___MIB_I.shtml
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MIB
• The excerpts in the text are from
– MIB-2 / system (Table 9.2, p. 772)
– MIB-2 / UDP (Table 9.3, p. 773)
• What was the point of all this?
– This gives the organization of all existing MIB
modules – e.g. so if you want to know what
TCP information is readily available, you can
find what has already been predefined
– This keeps you from reinventing the wheel!
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SNMP Protocol Operations
• The purpose of SNMP is to exchange MIB
information between agents and managing
entities, or between two managing entities
• Much of SNMP works on request-response
mode – the managing entity requests data, and
the agent responds with that data
• Problems or exceptions are reported with a trap
message – they go just from agent to managing
entity
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SNMP Message Types
• SNMP messages are called PDUs
(protocol data units) (RFC 3416)
• There are seven types of PDUs (p. 790)
– From manager (managing entity) to agent
there are three kinds of GetRequest (to read
agent data), plus SetRequest (to set the value
of agent data)
– From agent to manager there is the SNMPv2Trap PDU to report exceptions (RFC 3418)
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SNMP Message Types
– From manager to manager there is an
InformRequest message to pass on MIB data
– And finally, most messages are responded
to using a … Response message
• We’re not going to dwell on the format of a
PDU message – it’s up to 484 octets long
• PDU messages should be sent over UDP,
per RFCs 3417 and 4789
– Also possible to send over AppleTalk, IPX, …
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SNMP Message Types
– SNMP listens on port 161 normally;
port 162 for trap messages
• Hence the sender needs to determine if
a Response was received or not
– RFCs are vague on retransmission policies
• SNMP is described across many RFCs
– The best place to start looking is RFC 3416,
which summarizes the SNMP Management
Framework
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Security and Administration
• This is a key area of improvement in
SNMPv3 over SNMPv2
• Managing entities run SNMP applications,
which typically have
– A command generator (create Get messages)
– A notification receiver (to catch traps)
– A proxy forwarder (forwards requests,
notifications, and responses)
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Security and Administration
• Agents have
– A command responder (answers Get
messages, and applies Set requests)
– A notification originator (create traps)
• Any kind of PDU is created by the SNMP
application, then has a security/message
header applied
– An SNMP message consists of (the
security/message header) plus (the PDU)
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SNMP Message Header
• The header consists of
– SNMP version number
– A message ID
– Message size info
– If the message is encrypted, then the type
of encryption is added, per RFC 3411
• The SNMP message is passed to the
transport protocol (probably UDP)
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SNMP Message Header
• From RFC 3411, “This architecture
recognizes three levels of security:
– without authentication and without privacy
(noAuthNoPriv)
– with authentication but without privacy
(authNoPriv)
– with authentication and with privacy
(authPriv)”
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SNMP Security
• Since SNMP can change settings (Set Request
message), security is very important
• RFC 3414 describes the user-based security
approach
– User name, which has a password, key value, and/or
defined access privileges
• Encryption (privacy) is done with DES symmetric
encryption in Cipher Block Chaining mode
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SNMP Security
• Authentication uses HMAC (RFC 2104)
– Take the PDU message, m, and a shared
secret key, K (can be a different symmetric
key than used for encryption)
– Compute a Message Integrity Code (MIC)
over the message AND the key K
– Transmit m and MIC(m,K)
– Receiver also computes MIC(m,K) and
compares it to what was received
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SNMP Security
• SNMP provides protection against
playback attacks by keeping a counter in
the receiver
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SNMP Security
• The counter acts like a nonce
– Actually tracks time since last reboot of
receiver and number of reboots since
network management software was loaded
(RFC 3414)
• If counter in a received message is close
enough to the actual value, treat the
message as a nonreplay (new) message
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SNMP Security
• Provides view-based access control (RFC
3415) by mapping which information can
be viewed by which users, or set by them
– In contrast with RBAC (role-based) or OBAC
(organization-based) access control
approaches
• Tracks this info in a Local Configuration
Datastore (LCD), parts of which are
managed objects (which can be managed
via SNMP)
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ASN.1
• We saw earlier that MIB variables are tied
to the ISO standard ASN.1
– It’s connected to XML and Bluetooth as well,
so it’s worth not ignoring
• It’s defined by ITU-T X.680 to X.683 and
ISO/IEC 8824
• Purpose is to describe data exchanged
between two communicating applications
– So it’s kind of a middleware for data exchange
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ASN.1
• Without ASN.1, it would be easy to define
dozens of logical approaches for
describing the contents of a data file, and
storing it
– ASN.1 gets everyone to agree how to do so
• ASN.1 tries to identify every possible
standardized object – no small goal!
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ASN.1
• Part of its need comes from the littleendian vs. big-endian problem
– Little-endian architecture stores the least
significant bit of integers first
• Intel and DEC/Compaq Alpha CPUs are
little-endian
– Big-endian stores the most significant bit first
• Sun and Motorola processors are big-endian
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ASN.1
• SMI and ASN.1 offer a presentation
service to translate between different
machine-specific formats
– This resolves the order in which bytes are
sent, so that something sent in ASN.1 format
from an Intel chip can be read correctly by a
Sun chip
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ASN.1
• ASN.1 provides its own defined data types
(p. 798), much like SMI (slide 47)
– Are used to create structured data types
• ASN.1 also provides various types of
encoding rules
– The Basic Encoding Rules (BER) tell how to
send data over the network (as in, byte by
byte), using the Type of data, its Length, and
Value (TLV)
• Data can be text, audio, video, etc.
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ASN.1
• Other type of encoding rules include
– Packed Encoding Rules (PER) – for efficient
binary encoding
– Distinguished Encoding Rules (DER) –
canonical encoding for digital signatures
– XML encoding rules (XER)
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Summary
• So in wrapping up, we’ve covered the ISO
outline of network management
– Fault, Configuration, Performance, Security, and
Accounting Management
• Seen network management infrastructure
elements and how they work in SNMP
– SMI to define data types, objects, and modules
– MIB to collect object data across the network
– ASN.1 communicates across hardware platforms
INFO 331 chapter 9
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