Computer Systems (III) - Networks Flashcards
What is a network?
Two or more electronic devices that are connected together for the purpose of communication
How are networks connected?
By a wired medium such as Ethernet cables or wireless medium, such as WiFi
What is a computer or device that is not connected to a network known as?
Stand-alone
List the advantages of networking devices
File sharing
Hardware sharing
Communication
Roaming access
List the advantages of networking devices on larger networks (businesses / schools)
Centralised maintenance and updates
Centralised security
User monitoring
Levels of access (different user rights)
List the disadvantages of networking devices
Cost
Management
Spread of malware
Hacking
What does LAN stand for?
Local area network
What does the following show?
A LAN
What are the properties of a LAN?
A LAN is a network that is geographically confined to one building or site
What does WAN stand for?
Wide area network
What does the following show?
A WAN
What are the properties of a WAN?
A WAN covers a large geographical area
Most WANs are made from several LANs connected together
The Internet is a global WAN
What is bandwidth when referring to network performance?
The amount of data that can be transferred at any given time, e.g. 500 Mbps
How can bandwidth, and therefore network performance, be increased?
Too many devices sharing the bandwidth of the network will cause congestion and slow performance
Bandwidth can be limited to devices
Wired (fibre versus copper) / WiFi signal can impact as can the hardware / topology
What hardware components are needed to connect a computer / device to a network?
Network interface controller (NIC)
Transmission medium (wired / wireless)
Connection point (router / hub / switch / WAP
What is a NIC?
Network interface controller (internal hardware allowing a device to connect to a network)
Can be separate cards but often built into the motherboard (wired / wireless)
What is a switch?
Switches connect devices onto a LAN
They receive data (units called frames) from one device and transmit this data to other devices
What is a router?
Routers transmit data between networks
Data (packets) are directed to their destination
They are used to connect LANs to the Internet
Name a common wired transmission medium for data transfer between computers
Ethernet (CAT 5e / CAT 6) – twister pair cables
Name a common transmission medium to carry a TV signal
Coaxial cable
How do fibre optics work and what advantages do they have?
Data transmitted as light – they suffer from no interference so can transmit over very large distances
*Are expensive
How does wireless work?
Radio waves transmit data
Wireless Access Point (WAP) devices allow connections (a switch)
Wireless subject to interference and limited range
What are the properties of WiFi?
Multiple devices to the same LAN
Range up to 100m
High bandwidth (for wireless)
Often used in the home (routers / desktops / laptops / smart TVs)
What are the properties of Bluetooth?
Direct connection between two devices
Range around 10m
Low bandwidth
Often found in headphones / wearables
What is a client-server network?
A network managed by a server, to which clients connect
Files and software stored centrally
Profiles / passwords to access
What are the advantages of a client-server network?
Easier to keep track of files
Easier to backup
Easier to install updates / network security
Reliable and always on
What are the disadvantages of a client-server network?
Expensive to setup
IT specialists needed to maintain
Server dependence – clients lose access if goes down
Server can become overloaded and slow
What is a Peer-to-Peer (P2P) network?
Devices all being equal, connecting directly
Files stored on individual devices, and shared
Often used in the home between devices / connect to a printer
What are the advantages of a Peer-to-Peer network?
Easy to maintain
No dependence – if one device fails, the whole network isn’t lost
What are the disadvantages of a Peer-to-Peer network?
No centralised management (security / backups more complicated)
Duplicates of files when copied between devices
Less reliable peer machines – one breaking may cause data loss
Machines slow when other devices access them
A device connected to a network is known as what?
A node
What is a network’s topology?
The arrangement of the network
What are the two most common network topologies?
Star topology
Mesh topology
What does the following show?
A star topology
What are the properties of a star topology network?
All nodes indirectly connect to each other (through switches)
The switch acts as a central point, through which all communications pass
What are the advantages of a star topology network?
Each node is separately connected – failure of one node doesn’t impact others
New nodes easily added
High performance – message passed only to intended recipient
What are the disadvantages of a star topology network?
Whole network fails if the switch fails
Lots of cabling is required - expensive
What are the two types of mesh topology?
Full mesh topology
Partial mesh topology
What are the properties of a mesh topology network?
No central connection point – each node is connected to at least one other node
Each node is capable of sending messages to and receiving from other nodes (nodes act as relays)
What does the following show?
Full mesh topology
Each node is connected to every other node
What does the following show?
Partial mesh topology
Not all nodes are connected directly (simpler, but data has further to travel)
What are the advantages of mesh topologies?
Messages received quickly if the route is short
Messages should always get through – many possible routes
No node should be isolated (multiple connections) and multiple connections = multiple transmissions
New nodes added easily
What are the disadvantages of mesh topologies?
Full mesh networks can be impractical to setup (high number of connections needed)
Many connections require a lot of maintenance
Where are mesh topologies commonly found?
Where reliability is very important:
Military organisations
Cities for traffic flow / sewage / lighting
Emergency services
Utility smart meters
What does communication require?
Rules – determining transmission speed / error checking / addressing methods etc…
What are rules that govern communication known as?
Protocols
What are the two main addressing protocols called?
Media Access Control (MAC)
Internet Protocol (IP)
What is MAC addressing and what are the properties of it?
Communications on the same network
Each device has a unique MAC address (assigned by the manufacturer)
MAC addresses are 48 or 64-bit binary numbers (converted to hexadecimal)
What are MAC addresses mainly used by?
Ethernet protocol on LANs – switches read the MAC address and direct the data to the correct device
What is IP addressing and what are the main properties?
IP addresses are used when sending data between TCP/IP networks (e.g. over the Internet)
IP addresses are automatically or manually assigned
IPv4 is 32 bit and IPv6 is 128 bit (allowing for 2128 unique addresses)
How does IPv6 work?
IPv6 addresses split into 16-bit chunks with each getting a hexadecimal
How does IPv4 work?
IPv4 addresses split into 8-bit chunks with each given as a denary
What is TCP/IP?
TCP/IP protocol dictates how data is sent between networks (e.g. the Internet) and is made of two protocols: TCP and IP
What is the TCP within the TCP/IP protocol?
Transmission Control Protocol – sets the rules for how devices connect (data split into packets / reassembling the data packets / checking the data is correctly sent and delivered)
What is the IP within the TCP/IP protocol?
Internet Protocol – directs packets to their destination across the network
What other protocols are built upon the TCP/IP to do specific Internet-based task?
HTTP (Hyper Text Transfer) – web browsers
HTTPS (HTTP Secure) – more secure HTTP protocol (encryption)
FTP (File Transfer Protocol) – access / edit / move files
POP3 (Post Office v3) – retrieves email (server holds until downloaded)
IMAP (Internet Message Access) – retrieves email (server holds until deleted)
SMTP (Simple Mail Transfer) – sends emails
Why do network protocols have layers?
Network protocols are divided into layers (a group of protocols which have a similar function)
Layers break communication into manageable pieces, can be changed without impacting other layers and standards force companies to make compatible, universal hardware and software
In a network protocol layer, how do the layers interact?
Layers are self-contained
Each layer serves the layer above it (e.g. layer 4 triggers an action on layer 3, which triggers an action on layer 2, which triggers an action on layer 1)
Draw an example of a 4-layer network protocol
What is the Internet?
A worldwide collection of networks – based on the TCP/IP protocol
What is the world wide web?
A collection of websites, hosted on web servers and accessed through the HTTP protocol
What are URLs?
Addresses used to access web servers and resources within them
What is the domain name service?
DNS translates the website domain name into IP addresses (so you can access www.tesla.com via this and not the IP address)
Domain Name Servers store the IP addresses and matching domain names
What is the cloud?
The cloud uses the Internet to store files and applications
It acts like an extension of traditional client-server networks
What are the advantages of the cloud?
Users can access files and applications from any connected device
Easy to increase storage and no expensive hardware needed
Backup and security provided + software updates
No need to pay for IT support staff
What are the disadvantages of the cloud?
Internet connection required
Dependent on the host for security / backups / updates + subscription fees can be expensive
Data can be vulnerable to hackers
Unclear on ownership over cloud data
What type of network attacks exist?
Active
Eavesdropping (passive)
External
Internal
What is an active network attack?
Active - where the hacker attempts to modify or delete data, or to prevent a network from operating correctly.
An example of this is denial of service (DOS) attacks on the internet, which use many internet enabled computers to force a web server offline.
What is a passive network attack?
Eavesdropping (passive) - where the hacker monitors a network in order to gain information.
An example of this is wiretapping, where communications are monitored.
What is an external network attack?
External - where someone outside of an organisation attempts the hack
What is an internal network attack?
Internal - where someone within an organisation attempts the hack
What network threats exist?
Malware Phishing Brute force Denial of service Data interception and theft Structured query language injection Poor network policy People
What is malware?
Malware is malicious software that is designed to hack a system.
Malware can take many different forms.
What is a malware virus?
Programs embedded (hidden) within other files. They replicate themselves and become part of other programs
Viruses often cause damage by deleting or modifying data
What is a malware worm?
Programs similar to viruses except that they are not hidden within other files
Worms often spread through emails.
What is a malware trojan?
Programs which pretend to be legitimate but in reality are malware. They are often disguised as email attachments
Trojans cannot spread by themselves - instead they deceive a user into installing the program
What is malware, spyware?
Programs that monitor user activities (such as websites visited, usernames and passwords used) and send the information back to a hacker
What is malware, ransomware?
Programs that attempt to blackmail a user into making a payment to a hacker
Some types of ransomware do little but try to scare users into paying, while others go further - they encrypt documents and will not decrypt them until a ransom is paid
What is Phishing?
Emails that try to trick users into giving away personal details. The phishing email pretends to be a genuine message and tries to deceive the user into following a link to a website that looks like the real company, for example, a bank. However, it is a fake website designed to catch data such as bank account numbers and security codes.
What is Brute Force?
Where a program is used to find a password by trying all possible combinations of characters until the correct one is obtained
What is Denial of Service?
Where a computer (or many computers) is used to prevent a server from performing its tasks. This is done by bombarding the server over and over again with requests
Eventually the server is tied up trying to handle all the DOS requests, making it very difficult for it to respond to legitimate requests
What is Data Interception and Theft?
Where data is intercepted during transmission. This is done using software called a packet sniffer, which examines data packets as they are sent around a network, or across the internet
The information gathered is sent back to a hacker
What is Structured Query Language (SQL) Injection?
Where SQL code is entered as a data input. Many databases use SQL code to interrogate the data and maintain the structure
SQL code can be inputted as data, which can cause errors or unintended operations
How can people become a network threat?
Where users do not adhere to network policy. People frequently ignore rules, or accidentally or deliberately break them. For example, many users choose easy to guess passwords, or send and receive personal emails which containing viruses
This behaviour increases the chances of a network being compromised and its data being accessed by unauthorised users (social engineering)
How is poor network policy a threat and what do these policies tend not to have?
Levels of access to prevent users from accessing sensitive data unless they are authorised to do so
Rules preventing external device connections
Regulation regarding secure passwords
Rules to govern what websites can be visited
Methods to prevent any user wirelessly connecting an unsecured device
Controls on what facilities can be accessed remotely (away from the organisation)
A formal backup procedure that is adhered to
A regular maintenance programme
What network security techniques are there?
Penetration testing Network forensics Network policies User access levels Secure passwords Encryption Anti-malware software Firewalls
What is penetration testing?
To determine how resilient a network is against an attack
It involves authorised users (sometimes an external party or organisation) who probe the network for potential weaknesses and attempt to exploit them. Software that enables network managers to test the resilience of networks themselves is also available
What are network forensics?
Monitoring the traffic on a network. At regular intervals transmitted data packets are copied
The copy and information about the packet are then stored for later analysis. This is usually processed in batches. The information gathered can help identify invasive traffic (from hackers) or to determine where data is being sent
What should a network policy ensure?
Passwords and securely and regularly changed
Users cannot connect unauthorised equipment
Levels of access are given, which allow only authorised users to access sensitive data
Regular backups / disaster recovery procedures + maintenance / anti-virus software
Regular penetration testing and forensic analysis
What is user access?
Access levels determine the facilities a user has access to, such as software, email, internet access, documents and data, the ability to install and/or remove software and the ability to maintain other users’ accounts
A network manager should make sure users can only access the facilities they need
What rules should exist around passwords?
Passwords help prevent unauthorized users accessing the network
They should be strong (letters, numbers and symbols) and regularly changed
What is encryption?
Translating data into a code which only someone with the correct key can access
During encryption, what terminology is used for the original text and the encrypted text?
Plain text becomes Cipher text
What is a firewall?
A tool that monitors traffic going into and out of a computer or network
What types of firewall exist?
Hardware-based or software-based
Hardware-based are more expensive but tend to be more effective
What is anti-malware?
Anti-malware includes anti-virus software, anti-phishing tools and anti-spyware software. It works by scanning through all the files on a computer and checking them against a list (known as definitions) of known malware.
It is reactive - it can only detect, prevent and remove known malware
