Networks Flashcards
Why do we connect computers in a network?
- To share data and software
- To share printers, hard drives and other hardware peripherals
- To enable people to communicate with each other using services such as email
What are properties of a LAN?
- Cover a small geographical area
- Managed by a local manager
- Owned by one person or an organisation
What are properties of a WAN?
- Cover a large geographical area to connect networks to each other
- Managed by several different people
- Collective ownership
How are computers addressed in the internet?
Most devices: Dynamic IP which changes each time they connect and reconnect to the internet
Routers and servers: Static IP which stays the same
What happens when a web page is requested?
- The user types a URL, which gets sent to a DNS server asking for its corresponding IP address
- The DNS matches the URL to the IP address and sends it to the browser
- The browser then sends the page request to the web server holding the page data
- The server finds the correct files and sends them to the browser which is then displayed
How does packet switching work?
- The sender’s file is broken up into packets
- The packets are directed to their destination by routers
- Packets take different routes across the network
- The receiving computer reassembles them in the correct order using information in the packet headers
What does a packet contain?
- Header
- Payload
- Footer
What does the packet header contain?
- Destination IP
- Source IP
- Packet number
- Checksum
What are the properties of copper wires?
- Up to 100m range
- Up to 10Gbps bandwidth
- Susceptible to electrical interference
- Used to connect devices in a LAN
What are the properties of fibre-optic cables?
- Up to 80km in range
- Up to 100Gbps bandwidth
- Immune to electrical interference
- Used for long distance data traffic
What are properties of Wi-Fi?
- Up to 100m range, but physical objects obstruct signal
- High power consumption
- Used to connect LANs and connect devices to the internet
What are properties of bluetooth?
- Up to 10m range
- Low power consumption
- Used to pair devices over short distances
What are properties of zigbee?
- Up to 100m range
- Low power consumption
- Used for home automation
What are properties of RFID?
- Up to 1m range
- Low power consumption
- Used in security tags, passports
What are properties of NFC?
- Up to 10cm range
- Very low power consumption
- Contactless payment systems
What is FTP?
File Transfer Protocol provides the rules for file transfer between computers
What is HTTP?
Hyper Text Transfer Protocol provides the rules to be followed by a web browser and web server when requesting and supplying information. Used to send requests and return web content
What is HTTPS?
Secure HTTP with encrypted communications between a host and client
What is SMTP?
Simple Mail Transfer Protocol which provides the rules for sending email messages from client to server and then from server to server
What is POP?
Post Office Protocol is used by a client to retrieve emails from a mail server which are downloaded and then deleted on the server
What is IMAP?
Internet Message Access Protocol is where you can read messages which are stored on a different server
What happens in the application layer?
Sending: Provides the interfaces and protocols needed by the user
Receiving: displays the received information to the user
What happens in the transport layer?
Sending: Splits outgoing data into packets and numbers them. Adds a header containing a sequence number and checksum and passes the packets to the internet layer
Receiving: Checks incoming packets and sends a resend request for any that have been damaged or lost in transport. Reassembles packets into the correct order and passes the data to the application layer
What happens in the internet layer?
Sending: Adds the source and destination IP address to packet headers, enabling routers to guide each packet to its destination
Receiving: Strips address information from incoming packet headers
What happens in the transport layer?
Sending: Uses network-specific protocols to convert binary data into electrical, light or radio signals for network transmission
Receiving: Converts incoming signals into binary data
What is a star topolgy?
Each computer is connected individually to a central switch
What are the advantages of a star topology?
- If a wire is damaged, the whole network will continue to function
- Data is only send to the intended computer directly
What are the disadvantages of a star topology?
- If the central point fails, then so will the entire network
- Requires a lot of cable because each computer is connected individually to a central component making it expensive
What is a mesh topology?
Each computer is connected to at least one other computer. As well as sending signals, each computer also relays data
What are the advantages of a mesh topology?
- Can handle high volumes of data
- If one component fails, there is always an alternative route for data
What are the disadvantages of a mesh topology?
- Expensive as lots of cable required
- Difficult to manage
What is a bus topology?
Each node is connected to a main cable called a bus with terminators on each end
What are the advantages of a bus topology?
- Easy to set up
- Easy to add extra devices
What are the disadvantages of a bus topology?
- Lots of data collisions occur when multiple devices transmit data at the same time
- If the main cable fails, the whole network fails
What is penetration testing?
Testers take the role of hackers to try and gain unauthorised access to a system or network to find vulnerabilities that can be fixed
What is black-box penetration testing?
Testers aren’t given any information about the network and have to use methods of a real hacker
What is white-box penetration testing?
Testers are given access to relevant network and system information and use this to identify potential security loopholes that could be exploited by people within the organisation
What is ethical hacking?
Hackers make attempts to penetrate a computer system or network on behalf of the owner to find security vulnerabilities
What is access control?
Where users are limited to who can log into a network and what they are permitted to do
What is physical security?
- Access doors should be kept locked and fitted with security recognition
- Biometric security recognition can be used on mobile devices to authenticate users
What are firewalls?
Software or hardware that prevents communications from entering the network
