university of worcester comp 1321 digital infrastructures week 9

University of WorcesterCOMP 1321Digital InfrastructuresWeek 9

Computer Networks

Presented by Lee Campbell

Learning

“If you can’t explain it simply, you don’t understand it well enough.”

Albert Einstein (1879-1955)

Lecture Topics

Lecture topics

The wonderful world of computer networking: An introduction to computer networks. Establishing connectivity. Network topology (physical and logical). Network hardware, network interface cards (NIC),

cabling, hubs, switches and routers. OSI model.

Today’s lecture

An Introduction to Computer Networks

What is a computer network?

Network (n & v) : A chain of interconnected computers, machines or operations.[The Concise Oxford Dictionary of Current English, 1990, Clarendon Press.]

What is a computer network? A network provides the transportation mechanism for the

exchange of data. Allows network devices to communicate. Computer networks were not designed with security in

mind. The network provides an adversary/threat the means to

achieve their required objectives. The end-points, applications and information also need to

be secured.

Google Data Centre

[http://cdn.slashgear.com/wp-content/uploads/2012/10/google-datacenter-tech-02.jpg]

[http://cdn.slashgear.com/wp-content/uploads/2012/10/google-datacenter-tech-02.jpg]

Google Data Centre

Google Youtube Data Center clip

The purpose of a computer network?

Three main purposes of a computer network.


[1] Provide connectivity: Internal and external (the Internet). Connecting network devices together. The Internet of Things (IoT). Location and mapping. Requires physical components to provide

connectivity. Cables, routers, hubs, repeaters, switches and power.


[2] Allows communication: Send emails, documents, files and information. Instant messaging, blogs, social media & web sites. Financial transactions. Video and audio streaming. Video and audio conferencing/broadcasting. Controlling cars and homes?


[3] Share resources: Information (many forms), documents and files. Banking and financial transactions. Music, photos and videos. Databases. Printers. Ideas, views and opinions.

Devices on the network

Network nodes, end-points, devices and computes: Traditional network devices:

Terminal, mainframe, server, workstation, PC and printer. Mobile Devices:

Notebook/laptop, smartphone, mobile phone, desktop Phone, PDA, watch and tablet.

Internet of Things (IoT): Freeze, cooker, heating, coffee machine, alarm system, home

automation (lights, video and music). Others.

The Internet – UK submarine cable map (2014)

[https://gigaom.com/wp-content/uploads/sites/1/2014/01/cable-map-uk.jpg?w=708&quality=80&strip=all]]

The Internet - submarine cable map

[http://static.independent.co.uk/s3fs-public/thumbnails/image/2014/03/11/13/submarine-cable-map-2014-x.jpg]

Submarine fibre cable

[http://incept.co/img/37EQHAIMED.jpg]

Establishing Connectivity

Comparison of the OSI and TCP/IP models

Physical

Data Link

Network

Transport

Session

Presentation

Application7

6

5

4

3

2

1

OSI Model

Network Access

Internet

Transport

Application

TCP/IP Model

4

3

2

1

Transmission Control Protocol - SYN, SYN-ACK and ACK

TCB : Transmission Control Block.Endpoint IP and PORT values, status of the connection and buffers. [http://www.tcpipguide.com/free/t_TCPConnectionEstablishmentProcessTheThreeWayHandsh-3.htm]

Open Connection Close Connection

TCP packet (Transport layer)

[http://courses.oreillyschool.com/sysadmin5/images/TCP-Header.png]

UDP packet (Transport layer)

[http://microchip.wdfiles.com/local--files/tcpip:tcp-vs-udp/TCP_UDP_headers.JPG]

IP packet (Network layer)

[http://courses.oreillyschool.com/sysadmin5/images/IP-Header.png]

TCP/IP Packet

The major TCP flags URG (1 bit) : Indicates that the Urgent pointer field is significant ACK (1 bit) : Indicates that the Acknowledgment field is significant. All

packets after the initial SYN packet sent by the client should have this flag set.

PSH (1 bit): Push function. Asks to push the buffered data to the receiving application.

RST (1 bit): Reset the connection. SYN (1 bit): Synchronize sequence numbers. Only the first packet sent

from each end should have this flag set. Some other flags and fields change meaning based on this flag, and some are only valid for when it is set, and others when it is clear.

FIN (1 bit): No more data from sender.

Ethernet Frame - 802.3 (Data-link layer)

[http://core0.staticworld.net/images/idge/imported/article/nww/2008/05/01fig95-100279181-orig.jpg]

Naming and Addressing (1)

All networks need a naming system. Names and numbers. No duplicates. LAN : Internal naming system (DNS, IP, Device Name). WAN : DNS, IP and Device Name. “Address” normally numerical. “Name” normally letters.

[Courtesy of R.Henson]

Naming and Addressing (2)

Fulfil the required purpose: Unique network identity for each device. Provides destination for data to be sent to. Provides source location for data sent.


Media Access Control (MAC) – Data-Link layer Naming

From first IEEE (802) spec…. use “hardware” (MAC) address of device

Data sent as “frames” transfer very fast…

Typical MAC address: xx.xx.xx.xx.xx.xx (where x= a hexadecimal number)


IP – Network Layer Naming

Originates from TCP/IP naming system: typical IPv4 name: x.x.x.x where x = a number, 0 to 255 decimal.

now IPv6 IPv4 running out of unique numbers!


Name Resolution

DNS (Domain Name Service/System): Domain name to IP. IP to domain name.

• NetBIOS names• Resolve NetBIOS name to IP address.

• WINS names (Windows Internet Name Service)• Resolve WINS name to IP address.

• ARP protocol• Resolves IP address to MAC address.• Reverse ARP (vice versa).


Network Practical

Please do not capture packets from the University network – only use the captured files provided in

Blackboard.Please do not compromise University policy in regard

to network usage and access.Wireshark is an open source tool. Please use for the

intended purpose.

HTTP Wireshark capture

Network Topology

Network topology

Topology (n) : The way in which constituent parts are interrelated or arranged.

Topologies can be either physical or logical in nature. Physical topologies describe how the physical cables run, and how these cables connect to the network

devices. Logical topologies describe the movement of data within the physical topology.

We need a way of describing the physical and logical nature of networks….

Five primary topologies

Bus topology Logical or physical.

Star topology Physical only.

Ring topology Logical or physical.

Five primary topologies

Mesh topology (partial and fully connected) Logical or physical.

Hybrid Physical.

Bus topology (1)

Star topology (2)

Ring topology (3)

Mesh topology (4.1)

Fully connected mesh topology (4.2)

Hybrid topology (5)

LAN, MAN and WAN Local Area Network (LAN):

Interconnecting network devices in a limited area, a building or buildings.

Metropolitan Area Network (MAN): A network that interconnects users in a geographical area or

region such as a town or city. A MAN is smaller than a WAN but bigger than a LAN.

Wide Area Network (WAN): A WAN spans a larger geographical area. Most WANs are

constructed from several LANs connected together.

LAN, MAN and WAN

[http://www.gta.ufrj.br/ensino/eel879/trabalhos_vf_2008_2/igorcamp/LAN_MAN_WAN.JPG]

Advantages and disadvantages of topologiesTopology Advantages Disadvantages

Bus Cheap and easy to install.Difficult to reconfigure and troubleshoot.

Media failure can impact the entire network.

Star

Cheap and easy to install. Easy to configure and fault tolerant.

Failure of the switch will impact the network.

More cabling, therefore more expensive than Bus.

Ring Efficient and easy to install.Difficult to install and reconfigure.

Media failure can impact the entire network.

MeshSimplest for data flow. Most fault tolerant

(fully connected). Provides redundant links.

Expensive due to the amount of cabling required.

HybridProvides a combination of the best

features. Costly if implementing Mesh topology.

LAN and WAN topologies

Local Area Networks (LANs) usually use a Star topology.

Wide Area Networks (WANs) usually use a Mesh topology.

Why?


Network Hardware

Physical components of a network (1)

Firewalls

Routers

Switches

[Images cursory of Cisco.]

Physical components of a network (2) Transmission media:

Copper cable, includes twisted pair, shielded twisted pair and co-axial. Optic fibre, radio waves and microwaves. Coaxial cable (copper):

Thinnet – 10Base5. Thicknet – 10Base2. Co-ax transmits around 10Mbps.

Twisted pair (copper): Unshielded Twisted pair (UTP). Shielded Twisted pair (STP).


[http://learn-networking.com/wp-content/uploads/2008/01/thicknet-thinnet1.jpg]

[https://upload.wikimedia.org/wikipedia/commons/9/9e/Network_card.jpg] [http://www.brainbell.com/tutorials/Networking/images/02fig04.gif]

[http://aqyro.com/blog/wp-content/uploads/2009/12/RJ-45_test_Studio08.jpg][http://www.digitus.info/typo3temp/pics/63af6e1734.jpg]


ST: Straight Tip SC: Subscriber/square/standard

Connector. FC: Fix Connector. LC: Lucent/Little Connector. MU: Miniature Unit. ESCON: Enterprise Systems Connection. MTRJ: Mechanical Transfer Registered

Jack. VF45: Volition Socket.

https://hookandy.files.wordpress.com/2011/06/fibre-connectors.jpg


[http://www.warrenandbrown.com.au/telecommunications/public/editor_images/61.jpg]


[https://www.ira.inaf.it/Computing/tecnica/FIBRE/fiber_files/fiber%2520diag2.jpg] [http://www.fiberonellc.com/wp-content/uploads/Singlemode-vs-]Multimode2.png]

Cables and Connectors

Types of Ethernet cabling: Twisted pair

Unshielded twisted pair (UTP) and STP Coaxial cable: single copper wire with braided

shield. Fibre-optic: glass strands inside protective tubing.


Ethernet types: 10 Mbps (Ethernet). 100 Mbps (Fast Ethernet). 1000 Mbps / 1Gbps (Gigabit Ethernet). 10000 Mbps/ 10Gps (10 Gigabit Ethernet/10GE,

10GbE or 10GigE).

Ethernet standard cable length and speed

[http://www.tardyslip.net/wp-content/uploads/2015/01/Ethernet-Cable-Length-and-Speed.jpg]

Ethernet standard cable length and speed

[http://www.belden.com/images/B29_Chart.jpg]


[http://www.cables-solutions.com/wp-content/uploads/2014/12/common-ethernet.jpg]

Networking standards Various network standards exist:

The Institute of Electrical and Electronics Engineers (IEEE). Based in New Jersey, USA.

802 is a group of network standards that deals with LAN and MAN networks.

802.3 – Wired Ethernet standard, includes LAN with CSMA/CD.

802.11 – Wireless networking standard. 802.4 – Token bus networks. 802.16 – Broadband Wireless Access (WiMAX certification).

OSIModel

Layered approach to networking In 1984 the International Standards Organisation (ISO) proposed the

Open Systems Interconnection (OSI) as a seven-layer network. The ISO model defined layers of abstraction for services, interfaces and

protocols. Services : Addressing, flow control, reliable delivery, connection control,

error control, segmentation and reassembly, multiplexing, latency optimisation and guaranteed delivery.

Interfaces: Provide connectivity between the layers. These are expressed as APIs between each layer.

Protocols: Provide the rules for governing communication. Provides addressing, initial hand-shake, final tear-down, transmission/receipt of information, unicast, multicast and broadcast. Sending, listening and waiting.

OSI Model

Physical

Data Link

Network

Transport

Session

Presentation

Application7

6

5

4

3

2

1

OSI Model

Binary transmission, physical characteristics, electrical and light signals, wires, connectors, distance and data rates. Topologies, Bus, Ring, Star and Mesh.

Transmits frames from host to host based on physical MAC addresses. Records start and end of frame. Also implements

flow control.

Routes packets based on IP addresses within/between LANs and WANs.

Responsible for delivery of streams. Provides ordered delivery, flow and error control.

Starts, stops sessions and maintains order.

Provides data conversion. Presents information in form meaningful to the application.

Defines the functions and services to run the network applications. HTTP for example, access web page and transfer

information to the web browser.

Description

Data Units and network devices

Physical

Data Link

Network

Transport

Session

Presentation

Application7

6

5

4

3

2

1

OSI Model

Packets

Frames

Bits

Segments

Data

Data Unit

Routers

Switches

Repeaters

Firewalls

Proxies

Network Devices

FirewallsProxies

Encapsulation

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application

DataDH NH TH SH PH AH DH

DataDH NH TH SH PH AH DT

DataNH TH SH PH AH

DataTH SH PH AH

DataSH PH AH

DataPH AH

DataAHConceptual flows

‘Real’ flow

Network models – applications and protocols

Physical

Network Access

Internet

Transport

Application

Data Link(MAC and LLC)

Network

Transport

Session

Presentation

Application

Ethernet

Token Ring

Frame

Relay

ATM

SONET

GSM

CSMA/CD

DSL

IP ARP ICMP IGMPRARP IPSec

TCP UDP

SMTP/ POP/ IM

AP

HTTP / HTTPS

DNS

WINS

Telnet / SSH

FTP / SFTP / SCP

10Base2

10Base5

10Base-T

100Base-TX

1000Base-T

10GBase-T

1000Base-SX

10GBase-SR

AppleTalk

DCCP SCTP

FDDI

ISDN

IPX/SPX

DHCP

LDAP

NTP

7

6

5

4

3

2

1

OSI Model TCP/IP Model

NetBIOS

PPTP

JPEG

GIFApplication

Network security taxonomy Technical vulnerabilities exist in the design, implementation and configuration.

Organisational vulnerabilities include people, processes and procedures. Header based

Modify the source and destination addresses, setting invalid bits in the header and sniffing the network to capture data. Examples DoS, DDoS and ARP broadcasts.

Protocol based Sending packets out of order, sending packets too fast and not sending packets. Example,

SYN flood attack. Attacker does not respond to SYN-ACK with ACK. Authentication based

Host-to-Host authentication not user to system. Based on IP and MAC addresses. Use IP spoofing and ARP poisoning.

Traffic based Too much data is sent to a layer/s. The layer/s cannot process the volume of data. Also,

packet sniffing, almost every protocol can be sniffed.

Attacks at different layers

Physical

Data Link

Network

Transport

Session

Presentation

Application7

6

5

4

3

2

1

OSI Model

Ping/ICMP flooding, IP spoofing and Routing (DV and LS).

ARP spoofing, MAC flooding and VLAN hopping.

Wire Tapping.

DNS poisoning, DNS zone transfer, FTP, Telnet and POP authentication information.

Attack

SYN Flooding, Session Hijack and Session Poisoning.

Function of the Application layer (layer 7) Interface for applications to use to gain access to network services:

Networked file transfer. Message handling. Database query processing.

Controls generalised network access: Supports applications which exchange data. Provides error & status information for applications.

If network is peer to peer: Authenticates peer partners. Determines if peers are ready to communicate.


Function of the Presentation layer (layer 6) Responsible (sending) for converting data from:

Application-specific format To a generic (machine-independent) format that can be passed across a

network Receiving

for converting incoming data from a generic format to one that makes sense to the receiving application

Also responsible for protocol conversion, encryption & decryption, and graphics commands

The redirector (software for handling service requests) also operates at this layer: If a service cannot be resolved locally, it sends the request out to the

network resource that can offer the required. [Courtesy of R.Henson]

Function of the Session layer (layer 5) Sets up a logical connection between machines called a

“session”, which allows networked resources to communicate. Manages the setting up of a user “session”, exchange of

information, and “tear down” as the session ends. Manages issues such as who may transmit data at a certain

time, and for how long, also ensuring that the system doesn’t “time out” after inactivity.

Ensures data is routed to the correct application on the local machine.

Synchronises services between tasks at each end of the communications channel in half duplex communications.


Function of the Transport layer (layer 4) Responsibilities:

Multiplexing. Connection management. Transport of data. Stream orientation.

The Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) operate at this layer.

Data units described as “segments”.

Function of the Network layer (layer 3)

Provides messages with an address for delivery (e.g. IP address).

Translates logical network addresses/names into physical equivalents.

Handles packet switching and routes packets to their destination on the local network.

Controls network packet congestion. Ensures packets conform to the network's format.


Function of the Network layer (layer 3)

Responsibilities: Packet (IP) addressing and sequencing. Determining to route from source to destination

computer. Routers operate up to this level.


Function of the Data-Link layer (layer 2) Responsible for error free physical transmission of data using frames. May include an error recovery mechanism and also a flow control mechanism,

although this may be done at the transport layer. Mechanism (down):

Data from the upper layer, the network layer, is converted by the data link layer into frames. The Logical Link Control (LLC) performs this function.

Mechanism (up): Arranges raw data bits received via the physical layer into frames, for passing on

to the network layer. The Media Access Control (MAC) performs this function. Framing, collision resolution and management of checksums.

Naming system for devices: MAC addresses. These are physical address uniquely assigned to the network interfaces.

Bridges and switches operate up to this layer.[Courtesy of R.Henson]

Function of the Physical Layer (layer 1) Responsible for communicating with the network

hardware. Bits are converted into electrical signals and vice versa. Issues include modulation of signals and timing. Manages the interface between a computer and the

network medium, but cable type and speeds of transmission are deliberately omitted to allow future technology to be easily included.

Repeaters work only at this level.[Courtesy of R.Henson]

Q&A

Thank You Everyone!

university of worcester comp 1321 digital infrastructures week 9

Documents