SLR11 - Networks

Networking advantages

• Share files

• Share peripherals & connect to networks e.g. internet

• Access files from any computer on network

• Server control security, software updates, backup

• Communicate

Network disadvantages

• Security risk - malware & viruses spread easier

• If server fail, computers may not work

• Computer may run slower if lot data travelling on network

Standards

• Set of hardware & software specifications

• Allow manufacturers to create products & services that are compatible with each other

• E.g. character set

Protocol

• Allow devices communicate

• By ensuring all follow same standards

8 Main Protocols

• TCP

• IP

• HTTP/HTTPS

• POP

• IMAP

• SMTP

TCP

• Transmission Control Protocol

• Provides error free transmission between two routers

IP

• Internet protocol

• Routs packets across a WAN

UDP

• User Datagram Protocol

• Simple connectionless transmission model

HTTP/HTTPS

• Hypertext Transfer Protocol / Secure

• Allow client & server to request and deliver HTML web pages / added encryption

FTP

• File Transfer Protocol

• Used to send files between computers, normally WAN

POP

• Post Office Protocol

• Retrieves emails from mail server and transfers them to device, removing them from server

IMAP

• Internet Message Access Protocol

• Keep emails on mail server, keeping devices in cync

SMTP

• Simple Mail Transfer Protocol

• Transfers outgoing emails between severs and from email client to servers

Internet

• Collection of interconnected networks, routers, cables

• Home network connected via typical wireless router

• Router connects to Internet Service Provider (ISP) via fibre optic

• ISP connected to DNS and other routers

Layering

Concept of layering is to divide complex task of networking into smaller, simple tasks that work in tandem with each other

Layering advantages

• Reduce complex problems to smaller sub-problem

• Devices can be manufactured to operate particular layer

• Products from different vendors work together

TCP/IP

• Transmission control protocols

• Protocols are set of rules of communication across internet

• Each protocol belongs to different layer

• Data further encapsulated as its passed to next layer

TCP/IP Layers

• Application

• Transport

• Internet

• Link

Application layer

• Network applications such as web browsers, or email programs operate at this later

• FTP, HTTP/S, SMTP, IMAP

Transport layer

• Sets up communication between two hosts - agree settings such as language & packet size

• TCP, UDP

Internet layer

• Addresses & packages data for transmission

• Routes packets across network

Link layer

• Network hardware & connection port standards

• Operating system device drivers also sit here

• Facilitates transmission of binary via any media

• Copper twist pair, fibre, Wi-Fi

MAC address

• Required when communicating on same LAN which only requires link layer

• MAC unique to each device

• MAC address can be found by sending request to all surrounding devices only devices with matching Ip respond, not possible on internet - too many devices

IP address

• Communication between two devices on different networks (WAN) requires both network layers, which uses IP address to create packets and link layer frame

• IP tells roughly where devices would be on internet

Sending over same network

• One host can send to another

• Host may need to broadcast first if MAC isn’t already known - ARP protocol used for this

• As traffic passes trough switch, it examines the source code and destination MAC and learns which address links to which device

Sending packets over networks

• Data transmitted via router

• Destination MAC address will be address of router when sending

• When frame reaches router, router works out where needs to send packets by looking at destination IP

• Router then sets own MAC address as source and next device as destination

• Router can also use ARP protocol to find destination MAC address if router doesn’t already know it

• If there are several routers on path to destination, source & destination MAC address will be overwritten at every hop

• Original message split apart and wrapped in segments which are wrapped in packets which are wrapped in frames

• Once arrive destination, will travel up through layer of TCP/IP stack in reverse order, stripping headers & tails as it goes on = destination receives message

World wide web

Collection of files with information stored in hypertext web pages hosted on web server

DNS

1. User request URL

2. Browser send domain name to DNS

3. DNS maps domain name to IP address & return it to browser

4. Request for web page or resource is sent to web server using IP address

5. Requested web page returned to clients web browser

LAN

• Local area network

• Network covering small geographical area, typically on single site

• All hardware owned to organisation using it

• Typically connected by;

  • UTP cable

  • Fibre optic

  • Wi-Fi

WAN

• Wide area network

• Collection of connected computer over large geographical area

• Multiple LANs in different areas are connected form WAN

• Infrastructure leased from telecommunication companies own & manage it

• Typically connected by:

  • Telephone lines

  • Fibre optic cables

  • Satellite links

Client server model

• Controls access & security for stored files

• Manages access to printer

• Provides email services

• Runs regular backups of data

• Client makes requests to server for data, connections & other services

Client server model advantages

• Easy manage file security

• Easier backup shared files

• Easier to install software updates to all computers

Client server model disadvantages

• Expensive

• Requires IT specialist to maintain

• Server single point of failure

• User will lose internet access if server fails

Peer to peer model

• Peer = computer connected to network

• Peer == other peers

• Peers send own files to each other

• Each peer responsible for own security

• Peer usually have own printer

• Peer can usually send print jobs to another peer to process, but that peer must be on

Peer to peer model advantage

• Easy maintain

• No specialist staff

• No dependence on single computer

• Cheaper

• No expensive hardware

Peer to peer model disadvantage

• Network less secure

• Users need manage own backup

• Can be difficult to maintain well-ordered file store

Circuit switching

• Creates temporary & dedicated link of fixed bandwidth between source & destination that only lasts until transmission is complete - physical pathway

• All packets use same path

• Reserves bandwidth in advance

• Can cause lot bandwidth wastage

• No store & forward transmission

• Guarantees quality of transmission though dedicated bandwidth

Packet switching

• No physical pathways - each packet takes own path

• Packets travel independently - breaks stream of data into smaller blocks

• Doesn’t reserve bandwidth = no bandwidth wastage

• Supports store & forward transmission

What is hacker

Individual attempts gain access to computer with intent of damaging data or harming system

Types of hackers

• Black hat hacker: Gain access via nefarious means, typically to steal company secrets or cause damage

• White hat hacker: Ethical hacking, use expertise to try identify & fix vulnerabilities

• Grey hat hacker: Attempt to locate flaws in company’s computer system without permission

Security issues & threats

• Malware

• Denial-of-service attack

• SQL injection

• Social engineering

Malware

Code written with intent to frustrate or harm

Types or malware

Virus: Piece of code capable of copying itself & spread through system, designed to corrupt file

Spyware: Covertly obtains information about user’s computer activity by transmitting data from their device

Denial-of-service attack

• Attacker floods server with useless traffic, exploiting TCP/IP stack

• Distributed denial-of-service (DDOS) attack occurs when multiple systems orchestrate synchronised DOS attack at single target

SQL injection

• Designed to exploit vulnerabilities in poorly coded database applications

• Code in entered into input box & executed by server

Social engineering

Manipulation techniques used to exploit human error, with aim to obtain private information

Types of social engineering

Phishing: Trick user into giving personal information by disguising as trustworthy source

Pharming: Malicious code installed on Pc/server misdirecting users to fraudulent websites without knowing

Methods of minimising & preventing threats

Firewall

Secure password system

Up to date software & anti-malware software

Proxies

Encryption

Firewalls

Software configured to only let certain types of traffic through to prevent:

• Unauthorised internet traffic from outside LAN

• Users in LAN from accessing prohibited parts of internet

Proxy

Physical device placed between network & remote source that manages traffic in and out of network

Encryption

Process of changing plain text to unreadable form, wont prevent hacking but makes it difficult for stolen data to be read

Why are people considered the weak point

• Not locking doors

• Not logging off

• Not encrypting data

• Sharing passwords

• Mitigated through training & education programs

Moden

• Transforms digital information from computer to analogue signals to transmit wirelessly

• Can also translate incoming analogue signal

• Modulates/demodulates electrical signal sent through phone lines

• Ports:

  • One connected to outside world

  • Ethernet connected to computer/router

Router

• Routes data between:

  • Devices on home network

  • Between devices on network and internet

• Modem connected to one port on router

• Other devices connected by other ports/wirelessly Wi-Fi

Cables

• Twisted pair

• Coaxial

• Fibre optic

Twisted pair

• Made up of pair of insulated copper wire

• Effected by noise from magnetic fields

• Affordable

• Low bandwidth

• Used for telephone networks, data networks, cable shielding

Coaxial

• Made up of solid conductor wire & layers of insulation

• Also affected by external magnetic fields, less that twist

• Moderate bandwidth & price

• Used for feedlines connected to radio transmission & receivers

Fibre optic

• Made of optical fibres bundled into single cable

• Immune to external magnetic field noise

• High bandwidth & price

• Used for long distance connections & data centres

Network interface card (NIC)

• Allows both wired & wireless communication between computers

• Is both physical & link layer

Wireless access point (WAP)

Device that creates wireless LAN by connecting to the router/hub via ethernet and projects Wi-Fi that is limited & affected by various materials

Hub

• Allows connect multiple devices to network

• Operates on physical layer & considered passive device - broadcasts transmissions received to all other connected devices

• Can cause network to become flooded with unnecessary traffic

Switch

• Also allow multiple device connect to network

• Operates on link layer & considered active device - can inspect transmissions & route them to correct device, reducing unnecessary traffic

• Faster than hub