1.3.3 Networks - Josh D Flashcards
What is a standalone machine?
A single computer not connected to any other computer
How is a network formed?
By connecting one computing device to another via cable or wireless
What are 5 important advantages of networks?
- Users can share files
- Users can share peripherals and internet connection
- Users can access files from other computers
- Servers can control security, updates and backups
- You can communicate with other people e.g. email
What are 3 important disadvantages of networks?
- Malware and viruses spread easily between computers
- Central dependency on server
- Computers may run slower with high network traffic
What is a standard and two important examples?
Standards are a set of hardware and software specifications that allow manufacturers to create products and services that are compatible with each other. E.g. character sets (ascii, unicode) and HTML
What is a protocol?
Protocols are a key way of ensuring technology-based standards are followed
What does the Transmission Control Protocol (TCP) do?
TCP provides error free transmission between two routers
What does the Internet Protocol (IP) do?
IP routes packets across a WAN
What does the User Datagram Protocol (UDP) do?
UDP is an alternative to TCP with no error checking (so it’s unreliable). It is a simple end-to-end connection model used to send short messages where speed is more important than accuracy (e.g. gaming).
What protocols are used for communication over LAN/WAN?
TCP, IP, UDP
What does the Hypertext Transfer Protocol (HTTPS) do?
HTTP allows client and server to send and receive requests.
Used to deliver HTML web pages. Fundamental protocol for WWW
What is the difference between HTTP and HTTPS?
HTTPS is the same as HTTP but involves encryption and authentication. The ‘s’ stands for secure
What protocol is used for sending files over a WAN?
File Transmission Protocol (FTP)
What is an FTP client?
An app that sits above the FTP protocol and generates the appropriate FTP commands automatically
What is the simple mail transfer protocol (SMTP)?
It transfers outgoing emails from clients to servers, and between servers
What is the post office protocol (POP)?
POP retrieves emails from a server and transfers it to your device. It is deleted from the server.
What is the internet message access protocol (IMAP)?
IMAP keeps emails on the server, maintaining synchronicity between devices. You view a copy of the email.
What is the Internet and the World Wide Web?
The Internet is a wide area network of WANs. WWW is a service on the internet. Internet ≠ WWW
What is the concept of layers?
To divide the complex tasks of networking into smaller simpler tasks that work in tandem with each other.
Each layer has a defined responsibility and each one provides a service to the layer above
What are 3 advantages of using layers?
- It reduces a complex problem into smaller sub-problems
- Devices can be manufactured to operate at a particular layer
- Products from different vendors will work together
What are the 4 layers in the TCP/IP stack?
Application, Transport, Internet and Link
What happens on the application layer?
Network applications (web browsers, email clients etc) use an appropriate protocol to transmit data
Give some examples of protocols that occur on the application layer
FTP, HTTP(S), STMP, IMAP, POP
What happens on the transport layer?
- Establishes a connection using UDP
- Data is split into packets
- Port numbers + sequence numbers are added to the packet header
What happens on the internet/network layer?
- Each packet receives a source and destination IP address
- Socket = IP + Port, e.g. 127.56.87.2:80
Socket tells us where to send the packet (IP) and to which application (port)
What happens on the link layer?
- Responsible for adding source and destination MAC addresses
- When data goes through multiple routers over a WAN, MAC addresses are changed at each hop
- “Packet” becomes a “frame”
What is a MAC address?
A 48 or 64-bit code assigned to each device by the manufacturer to uniquely identify the device
IP addresses AND MAC addresses are used for communication over a [LAN/WAN/both]
Both.
Although communication over a LAN only requires MAC addresses, modern LANs use IP addresses treating it as if it were a WAN
What is broadcasting?
When a MAC address is unknown, the data is sent to all devices on the network. The correct device will accept the data, and the switch will store the MAC address with its corresponding device eliminating the need for future broadcasting
What is the World Wide Web?
WWW is a collection of hypertext files and other files hosted on web servers
What is the role of web servers in the World Wide Web?
Web servers host/store hypertext files (and other files) and handle client requests by sending the files to the client
How does typing a URL lead to loading a web page? (5 steps)
- User requests a URL via a browser
- Browser sends domain name to Domain Name System (DNS)
- DNS maps domain name to an IP address
- Browser can send GET request to web server using the IP address
- Web page is returned to browser
How does the Domain Name System work? (in other words how does the DNS take a URL and give an IP address) (8 steps)
- URL received by DNS resolver server (e.g. www.google.com)
- … which queries a DNS root name server
- … that responds with address of top-level domain server (TLD) for .com
- Resolver makes a request to the (.com) TLD server
- … which responds with IP address of the domain’s name server (google.com)
- Resolver server queries domain’s name server
- … which returns google.com’s IP address
- … so the Resolver server can give the browser the IP address of google.com
What is a Local Area Network (LAN)?
Any network that covers a small geographical area usually on a single site.
The hardware tends to be owned by the organisation using it
What is a Wide Area Network (WAN)?
Any network that covers a large geographical area.
WANs are formed when multiple LANs are connected together.
The infrastructure used in a WAN is leased from telecommunication companies
What is circuit switching?
When you create a temporary dedicated link of fixed bandwidth that lasts until transmission is complete
What is the main pro and main con with circuit switching?
Pro: Guarantees quality of transmission (perfect for an end-to-end link)
Con: Lots of wasted potential bandwidth
What is packet switching?
When you break streams of data into smaller blocks, each sent independently of one another.
At each node packets are sent down the least congested route
What is the main pros and main con with packet switching?
Pro: More efficient and affordable as all bandwidth can be used at once
Pro: Can easily respond if parts of the network fail
Con: Doesn’t guarantee quality transmission (packets can be lost and arrive out of order)
Why do we need network security?
To only let authorised users access what they need, prevent unauthorised access and minimise the damage caused by unauthorised access
Define hacker
Someone who attempts to gain access to a computer system with the intent of damaging data or harming the system
What is a black-hat hacker?
A hacker that attempts to gain access via nefarious means usually to steal data or cause damage
What is a white-hat (ethical) hacker?
A hacker employed by a company to hack their system to find and report vulnerabilities
What is a grey-hat hacker?
A hacker who illegally gains access to a system but reports the issue to the company
What is malware?
Any code written with the intent to harm
What are common effects of malware?
Deleting/corrupting/encrypting data, crashing computers, reducing network speeds and keylogging (and sending key logs to hacker)
What are viruses?
Viruses are pieces of code that copy and spread themselves, designed with a detrimental effect
What is spyware?
Malware that gathers data about a user. It can harvest browsing habits, email addresses, passwords etc
What is denial of service (DoS) attack?
DoS attacks are when an attacker floods a server/network with useless traffic, overloading it.
Why are DoS attacks such a problem?
They cost time and money to deal with
What is a distributed denial of service (DDoS) attack?
When multiple devices attack a server all at once. Usually a hacker infects devices which unknowingly become ‘zombies’
What is SQL injection?
A code injection used to attack poorly coded database programs, code is entered into a text box and executed by the server
What is social engineering?
Manipulation techniques that exploit human error, luring users to exposing data, spreading malware or providing access to a system
What is phishing?
When cybercriminals trick users into giving personal info by pretending to be a trustworthy source
What is pharming?
When malicious code installed on a PC or server redirects users to malicious websites without their knowledge or input. AKA “Phishing without the lure”
What is a firewall?
A software or hardware (or both) that only lets certain traffic through. It blocks certain ports and certain types of traffic. It can also inspect traffic to see if it is suspicious
What are the 2 main roles of firewalls?
- Prevent unauthorised incoming traffic
- Prevent prohibited outgoing traffic (e.g. blocking certain websites)
What are secure password systems?
They prevent unauthorised access. They can be made more secure by implementing password rules
What is the downside with robust secure password systems?
Too many strict rules cause users to write down their password so they don’t forget. This defeats the point of passwords
What does anti-malware software do?
It detects malware. It comes pre-installed.
