1.3 Networks

• Firewall:

  • Software that monitors and filters packets going to and from a network
  • used to prevent unauthorised access to a network
  • compares packets entering network against set of rules made by firewall software
  • these rules are called packet filters
• Router:

  • Provides internet access by forwarding data packets to the correct destination
• Fibre optic cable:

  • Made up of very thing optical fibres bundled together into a single cable
  • Cables can be either glass or plastic threads
  • Most expensive transmission media
• Coaxial cables:

  • 4 pairs of copper wire wrapped around each other to reduce internal interference
  • Cheapest transmission media
  • Less affected by external interference then twisted pair
• Twisted pair cables (Ethernet):

  • Made up of a single copper wire surrounded by a plastic layer for insulation and a metallic mesh to reduce interference
• Network interface card (NIC):

  • Hardware device required which allows a computer to connect a network using the Internet Protocol
  • assigns unique MAC addresses to each device (12 digit HEX number)
  • Both a physical and data link layer
• Wireless Access Point (WAP):

  • A device that allows other devices to connect to a network using standards such as Wi-Fi or bluetooth
• Hub:

  • Allows you to connect multiple devices to one network
  • Broadcast the transmissions it receives to all other connected devices
  • Slower then switches in terms of data transfer
• Switch:

  • Joins devices together on a LAN
  • Receives packets/data and sends them
  • Uses MAC address to establish a link between devices
  • Outputs data to the specific computer device
  • (directs flow of data across a network)
• Malware can:

  • Delete, corrupt or encrypt files
  • Cause computers to crash
  • Reduce network speeds
• Virus:

  • Code capable of spreading themselves spreading through a system
  • Corrupt files or destroys data
  • Only spreads when the user propagates it
• Spyware:

  • Form of malware
  • Obtains information about a user's computer activities by transmitting data from their device
  • Suck as keystrokes and browsing history
• Worm:

  • Form of malware
  • Self-replicating
  • Does not need a host program to propagate it
• Trojan:

  • Type of malware that disguises itself as a legitimate program
  • Can steal data/ create back-doors for attackers
• DDOS(Denial of service attack):

  • Floods a server with useless traffic
  • Causing the server to become overloaded
• SQL injection:

  • Entering SQL code into vulnerabilities in database applications
  • Entered into input text boxes and then executed by the server
• Phishing:

  • Online fraud technique to trick users into giving out personal information
  • Disguise themselves as a trustworthy source
• Pharming:

  • Malicious code installed on a PC or server misdirects users to fraudulent websites without their knowledge
• Anti-malware software:

  • Preventing and minimises malware
• Proxies:

  • Proxy is a physical device placed between a network and a remote source
  • All traffic travels through the device on its way in and out of a network
  • Benefit: proxies can reduce web traffic
  • Benefit: privacy of user is protected and they remain anon
• Firewalls are used to:

  • Prevent unauthorised access to a network access
  • To restrict applications that are used internally that have internet
• • Physical topology describes how the devices are physically connected
  • Logical topology describes how the devices communicate across the physical topologies
• Physical protocols - Rules which govern the physical mediums through which the data is travelling, such as:

  • Wired or Wireless
  • Serial or parallel data transmission
  • Copper or fibre optic cabling
• Logical protocols - Rules which govern the data being sent, such as:

  • Bit rate
  • Packet size
  • Ordering of packets
  • Routing
  • Compression and encryption
• Standalone machine:

  • A single computer not connected to anything else
• Advantages of a network:

  • Users can share file
  • Users can share peripherals and connections to other networks such as the internet
  • Users can access files from any computer on the network
  • Servers can control security, software updates and backup of data
• Disadvantages of a network:

  • Increased security risks to data
  • Malware and viruses spread very easily between computers
  • Computers may run slower if there is a lot of data travelling on the network
  • Increased hardware cost
• Standards:

  • A set of hardware and software specifications that allow manufactures to create products and services that are compatible with each other
• Protocol:

  • A set of rules needed to govern how data is sent and communicated between devices on a network
• TCP:

  • Transmission Control Protocol
  • Provides error-free transmission between 2 routers
• IP:

  • Internet Protocol
  • Routes packets across a WAN
• HTTP:

  • Hypertext Transfer Protocol
  • A way for a client and server to send and receive requests and deliver HTML web pages
  • Fundamental protocol for the World Wide Web
• HTTPS:

  • Hypertext Transfer Protocol Secure
  • Same as HTTP but adds in encryption and authentication
• FTP:

  • File Transmission Protocol
  • Used for sending files between computers, normally on a WAN
• SMTP:

  • Simple Mail Transfer Protocol
  • Transfers outgoing emails between servers and from email clients to servers
• POP:

  • Post Office Protocol
  • Retrieves emails from a mail server and transfer them to your device
  • Removing them from the server in the process
• IMAP:

  • Internet Message Access Protocol
  • Keeps emails on the mail server
  • Maintaining synchronicity between devices
• Why are protocols important on a network:

  • Allow devices to communicate
  • Ensures all devices follow the same standards
  • So they interpret signals in the same way
• Server:

  • A device which provides a central point of access
  • Responding to client's requests
• LAN:

  • A group of devices
  • Connected over a small geographical area
  • Using own internal infrastructure to send data
  • maintained by organisation using it