CSC 382: Computer SecuritySlide #1 CSC 382: Computer Security Network Security.
1.Computer Network
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COMPUTER NETWORK
Instructor:
Niranjan Baral
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Computer Network
A computer network is a collection of autonomous computer and other computing
hardware devices that are interconnected by a
single technology through communication
channels to facilitate communication and
resource-sharing among a wide range of users
Communication channels : Copper wire, optical
fiber, microwaves, communication satellite
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Advantages of Networking
Easy Communication and Speed
Share Files, Data and Information
Sharing Hardware and Software(so Cheap) Supports the way we live, the way we learn and
the way we work .
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Disadvantages of Networking
Security Issues
High installation cost
Breakdown of the whole network Bandwidth Issues
Need of skilled human resources
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Uses of Computer Network
1. Business Applications
Resource Sharing(Both Hardware and Software)
Communication medium among employees Videoconferencing
Electronic business(E-Commerce)
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Uses of Computer Network cont..
2. Home Applications
Access to Remote Information
Person to Person Communication Entertainment
Electronic Commerce
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Uses of Computer Network cont..
3. Mobile Users
Portable electronic equipment as notebook to
send and receive telephone calls, mail, forweb surfing, access remote files and log on to
remote machines
Use wireless Network
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Networking Models1. Client Server Model
Network architecture in which each computer or process on the
network is either a client or a server. client host requests, receives service from always-on
server e.g. Web browser/server; email client/server
Servers are powerful computers or processesdedicated to managing disk drives (file servers),printers(print servers), or network traffic (networkservers ).
Clients are PCs or workstations on which users runapplications. Clients rely on servers for resources, suchas files, devices, and even processing power.
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Client Server Model cont
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PC running
Explorer
Server
running
Apache Web
server
client: browser that requests,
receives, displays Webobjects
server: Web server sends
objects in response to
requests
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Networking Models cont..2.Peer to peer model:
Distributed network architecture
in which individual nodes in the
network (called "peers") can act
as both suppliers and consumers
of resources, no use of dedicated servers
e.g. Skype, BitTorrent
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client/server
peer-peer
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Active Network
It has a set of 'Active Nodes' that perform customized
operations on the data flowing through them.
Traditional data networks provide a transport
mechanism to transfer bits from one end system to
another, with a minimal amount of computation(e.g., header processing and signaling).In contrast to
that active networks not only allows the network nodes
to perform computations on the data but also allowtheir users to inject customized programs into the
nodes of the network, that may modify, store or
redirect the user data flowing through the network.
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Active Network Cont.. This enables such ideas as sending code along with
packets of information allowing the data to change its
form (code) to match the channel characteristics.
Example: there may be a video multicast session where
at every node the video compression scheme is
modified, based on the computation done by that nodeand depending on the network bandwidth available.
Applications such a packet filtering in firewalls (also
routers) where the filters in the firewall decide whichpacket should go through and which should be blocked.
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PROTOCOLS AND STANDARDS
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Whats a protocol?
human protocols: whats the time?
I have a question
introductions
specific msgs sent
specific actions taken
when msgs received, or
other events
network protocols: machines rather than
humans
all communication activity
in Internet governed byprotocols
protocols define format, order ofmsgs sent and received amongnetwork entities, and actionstaken on msg transmission, receiptof a message or other event
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Protocols cont
Networking protocol is a set of rules that governs thedata communication and describe processes such as
The format or structure of the message
The method by which networking devices shareinformation about pathways with other networks
How and when error and system messages are
passed between devices The setup and termination of data transfer sessions
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Key Elements of Protocols1. Syntax: Structure or format of data. It refers the
order in which data are processed.(eg: first 16 bitsgive address of sender, following 8 bits message tobe sent and so on)
2. Semantics: Meaning of each section of bits. How aparticular pattern to be interpreted and what actionto be taken on interpretation.(eg: An addressspecifies route to be taken or final destination)
3. Timing: When and how fast data is to be sent.(eg:When a sender produces a data at 100 Mbps andreceiver receives at 1 mbps, overload and data lostoccurs)
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STANDARDSNeed of Standards:
Create and maintain open and competitive market forequipment manufacturers.
Guarantee Interoperability
Give a fixed quality and product to customers
To aid to design and implementation ideas To Provide guidelines to manufactures, vendors, government
agencies and service providers.
Categories:
De-facto( from the fact and not been approved by an organizedbody. Adopted as standards through widespread use)
De jure( legislated by a officially recognized body)
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Some Standards Organization
ITU( International Telecommunications
Organization)
IEEE( Institute of Electrical and Electronics
Engineer)
ISO: International Organization For
Standardization
IETF: Internet Engineering Task Force
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Reference Models
1. OSI Reference Model
2. TCP/IP Reference Model
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Layered ArchitectureOrganization of air travel
a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
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ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departure
airportarrival
airport
intermediate air-traffic
control centers
airplane routing airplane routing
ticket (complain)
baggage (claim
gates (unload)
runway (land)
airplane routing
ticket
baggage
gate
takeoff/landing
airplane routing
Layering of airline functionality
Layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
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Layered Architecture contAdvantages:
Reduced Complexity(complex system broken downinto smaller and understandable pieces)
Modular Engineering(Dividing a large work into
smaller modules) Interoperable Technology(Provide common language
to describe networking functions and capabilities)
Accelerated Evolution Prevent s technology or capability changes in one
layer from affecting other layers above and below.
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Basic Principles of layered Approach A layer should be created where a different level of
abstraction is needed. Each layer should perform a well defined functions.
The function of each layer should be chosen with aeye towards defining internationally standardized
protocols. The layer boundaries should be chosen to minimize
the information flow across the interfaces.
The number of layers should be large enough that
distinct functions need not be thrown together in thesame layer out of necessity and small enough that thearchitecture does not become unwieldy.
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Interface and Services Between each pair of adjacent layers is an interface.
Interface defines which primitive operations and
service the lowest makes available to the upper one
Service is a set of functions offered by a layer to the
upper layer in the protocol hierarchy.
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Open Systems Interconnection (OSI)
Reference Model Developed by ISO(International Organization for
standardization.
Called ISO-OSI Reference Model because it deals
with connecting open systems-that is, systems thatare open for communication with other systems.
The OSI model is not a network architecture - it
does not specify the exact services and protocols. Itjust tells what each layer should do.
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OSI Reference Model
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OSI Reference Model
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Ph i l L
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Physical Layer
The Physical layer controls how data is placed on
the communication media. The role of the OSI Physical layer is to encode the
binary digits that represent Data Link layer frames
into signals and to transmit and receive these
signals across the physical media - copper wires,
optical fiber, and wireless - that connect network
devices.
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Physical Layer cont.Major Responsibilities:
Define physical characteristics of Interfaces between
the devices and transmission media and defines thetype of transmission medium.
Data Rate
Bit Signal Representation: Representing the bits bysignal( electrical, optical or electromagnetic)
Bit synchronization( By providing the clockingmechanism between sender and receiver)
Multiplexing
Devices: Hubs, Repeater
Protocols: RS-232, T1, E1
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D t Li k L
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Data Link Layer Responsible for reliable and error-free transmission of
packets across a single link. It controls how data is placed onto the media and is received from the media
Framing: Determine the start and end of the packets Error detection :Determine which packets contain
transmission errors
Error correction: Retransmission schemes (Automatic Repeat
Request (ARQ) Flow control and Access Control
Physical Addressing
Packet Data Unit( PDU): Frame
Protocols: HDLC, PPP, Frame Relay
Devices: Bridges, Switches
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Data Link Layer ..SUBLAYERS:
Logical Link Control
Logical Link Control (LLC) places information in the frame thatidentifies which Network layer protocol is being used for theframe. LLC header tells what to do with a packet once a frameis received.This information allows multiple Layer 3 protocols,
such as IP to utilize the same network interface and media.
Media Access Control
Media Access Control (MAC) provides Data Link layeraddressing and delimiting of data according to the physicalsignaling requirements of the medium. It defines how dataare placed on media
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Network Layer The Network layer manages devices addressing, tracks
the location of device on the network and provides
services to exchange the individual piece of data overthe network. It provides internetworking i.e logicalglueing of heterogeneous physical networks together tolook like a single network to upper layers.
To accomplish end to end transport, Network layer usesfour basic process:
1. Addressing: Identification of each node or end deviceson a network with unique logical address i.e IP
address.2. Encapsulation: The Upper layer segment is
encapsulated with source and destination addrss toform a packet.
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Network Layer
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Network Layer..3. Routing: Finding the best path between source and
destination using different routing algorithm.
4. Decapsulation: In the receiver side, packets are
stripped off the logical address to reveal data
segments and passed to upper level.
PDU: packet
Devices: Router
Protocols: IP, ICMP, Apple talk, RIP
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T t l
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Transport layerThe basic function of transport layer is to accept the data
from the session layer, split it up to the smaller units if
need arises, pass these pieces to the network layer toensure that all pieces arrive correctly at the end.
Major Responsibilities:
Port addressing: Transport layer header includes a portaddress to allow multiples process on computers run atsame time and deliver the message from a specificprocess on one computer to specific process on other.
It tracks individual conversation Segmentation and Reassembly: Segments the data,
give sequence number so that it can be reassembled atreceiver side without error.
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T t l
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Transport layer Connection Control: Connection oriented or
Connectionless transfer of data.
Error Control: The transport layer makes sure that
the entire message arrives at the receiving tx layer
without error.
PDU: Segments
Protocols: TCP, UDP
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Session Layer:Allow users on separate machine to define how data
conversations are established, controlled and terminated.
Major responsibilities:Dialog Control: Keeping track of whose turn is to transmit. It
coordinates between system and servers to organize theircommunication by offering 3 different modes: simplex, Half
duplex or Full duplexToken Management: to prevent two parties from attempting
the same critical operation at same time.
Synchronization: Checkpointing how long transmissions to allow
them to continue from where they were before they crash.Protocols: RPC(Remote Procedure Call), Net Bios
PDU: DATA
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P t ti L
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Presentation LayerPresentation layer deals with the presentation of data and is
concerned with syntax and semantics of information
transmitted.Major tasks:
Translation: Networks can connect very different types ofsystems together which may have many distinctcharacteristics and represent data in different ways. Thepresentation layer handles the job of hiding these differencesbetween systems.
Encryption and Decryption
Compression
PDU: DataProtocols: JPEG, ASCII, MP4
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A li ti L
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Application LayerOSI model explains application layer as being the user
interface. The OSI application layer is responsible for
displaying data and images to the user in a human-
recognizable format and to interface with the
presentation layer below it.
Application layer provides interface between theapplications we use to communicate and the underlying
network over which our message are transmitted.
PDU: Data
Protocols: HTTP, DNS, FTP
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TCP/IP d l
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TCP/IP modelARPANET(Advanced Research Project Agency Network) was a
research network sponsored by DOD(Department of Defense,
US). It connected hundreds of universities and governmentsnetworks. When satellite and radio networks were addedlater, the existing protocols had trouble internetworking withthem, so a new architecture was needed.
So, to connect multiple networks in a seamless way was one
of the major designs goals of TCP/IP from the very beginning.Another goal was to survive the loss of subnet hardware of anetwork i.e DoD wanted connections remain intact as long assource and destination machines were functioning even ifsome of the intermediate devices or transmission lines were
kept out of operation. And a more real time architecture wasfelt necessary to transfer files and speech. TCP/IP wasdeveloped as an open standard. This speed up thedevelopment of TCP/IP as a standard .TCP/IP is named aftertwo of the popular protocolsTCP and IP.
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TCP/IP model
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TCP/IP model..
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TCP/IP M d l
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TCP/IP Model.. TCP/IP model describes the functionality of the protocols that makes the
TCP/IP protocol suite. Those protocols which are implemented in bothsending and receiving ends to provide end to end delivery.
Acomplete communication process includes these steps:1. Creation of data at the application layer of the originating source end device
2. Segmentation and encapsulation of data as it passes down the protocolstack in the source end device
3. Generation of the data onto the media at the network access layer of the
stack4. Transportation of the data through the internetwork, which consists ofmedia and any intermediary devices
5. Reception of the data at the network access layer of the destination enddevice
6. Decapsulation and reassembly of the data as it passes up the stack in thedestination device
7. Passing this data to the destination application at the Application layer ofthe destination end device
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TCP/IP Protocol Family
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TCP/IP Protocol Family
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Network Access
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Network AccessThe physical and Data link layer of OSI model is grouped to
form network access(interface) layer which involves
primitive bits that are transmitted on communicationchannels. It provides mechanical, electrical and functional
means and processes required for data transmission. It
provides a correct channel for transmitting data by
implementing error detection, error correction andsynchronization. It is also responsible for flow control. This
describes hardware requirements as pin configurations,
voltage levels and cable requirements.
Protocols: Ethernet, Frame Relay, RS-232, RJ-45
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Internet Layer
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Internet Layer Similar to Network layer of OSI model
The internet layer encapsulate the data into IPdatagram to include source and destination
address. The network layer checks network
topology to determine the optimal route for
message transmission, and transfers data. The key
factor is to determine the best route for
transmitting data packets from the source end to
the destination end.
Protocols: IP, ICMP
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Transport layer
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Transport layer
The basic function of the transport layer is toimplement end-to-end communication for the
application program between two hosts.
The transport layer receives data from theapplication layer, and then divides it into smaller
units if necessary. Before sending it to the networklayer, the system ensures that the data is sent tocorrect segments of the peer.
Protocols : TCP and UDP (User Datagram Protocol).
TCP reliable and connection oriented
UDP: does not perform end to end reliability check
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Application layer
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Application layer Include application, presentation and session layer of OSI
model.
The application layer is responsible for processing details ofa specified application program. The application layer
displays received information, transmits user data to the
lower layer and provides network interfaces for application
software. It includes a number of protocols that provide specific
functionality to a variety of end user applications and
defines how host programs interface with transport layer
services to use network.
Protocols: HTTP, TELNET, FTP, DNS
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Comparision of OSI vs TCP/IP model
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Comparision of OSI vs TCP/IP modelSimilarities:
Both are based on concept of stack of
independent protocols.
Both are layered approach. Functionality of the layers is roughly similar.
Both have comparable Network and Transport
layer.
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