1.3.3 Networks Flashcards
1
Q
Stand alone machine
A
A single computer not connected to anything else
2
Q
NETWORK advantages
A
- users can share files
- users can share peripheral devices and connections to other networks such as the internet
- servers can control security, backup of data and software updates
3
Q
NETWORK disadvantages
A
- increased security risks to data
- malware and viruses spread more easily between computers
- if a server fails, the computers connected to it may no work
- computers may run slower if there is lots of data travelling on the network
4
Q
Standards
A
- a set of guidelines/conventions that govern how a task should be performed or how a product should function
- a set of hardware and software specifications that allow manufacturers to create products which are compatible with each other
5
Q
NEED for standards
A
- standards enable different network devices regardless of their manufacturer of model to work seamlessly together .
6
Q
Protocols
A
- a set of rules to govern the transmission of data between devices [1]
7
Q
Why are protocols important in a network ?
A
- protocols ensure that all devices follow the same rules and standards [1]
- so that they interpret data and signals in the same way [1]
8
Q
Examples of protocols
A
- HTTPS (hyper text transfer protocol secure)
- HTTP (hyper text transfer protocol )
- TCP (transmission control protocol
- IP (internet protocol)
- FTP (file transfer protocol)
- SMTP (simple mail transfer protocol)
- IMAP (internet messenger access protocol)
- POP (post office protocol)
- UDP (user diagram protocol)
9
Q
What is a Logical protocol ?
A
- a set of rules that govern the transmission of data [1]
- these rules specify how data is represented [1]
- examples include character sets [1]
10
Q
TCP/IP
A
- a networking protocol used in the routing of packets through networks
- purpose : communication over LAN/WAN
11
Q
HTTP
A
Used for webpage rendering/requests
12
Q
HTTPS
A
- a version of HTTP (also used for webpage rendering/requests) but with encryption for security
- used for secure transactions like online banking and shopping
13
Q
FTP
A
- used for transmission of files over networks
- provides authentication (username and password)
- can manage file directories
14
Q
SMTP ( IMAP and POP are also used )
A
the standard for sending email messages between servers
15
Q
Physical topology
A
- The physical layout of wires and components which form the network
- eg bus, mesh, star
16
Q
logical topology
A
- the way data flows around a network
17
Q
BUS topology
A
- a network topology where all computers are connected to a single cable
- the ends of the cable are plugged into a terminator
18
Q
Bus topology advantages
A
- cheaper to set up ( as it requires less cable)
- doesn’t require any additional hardware
19
Q
Bus topology disadvantages
A
- if the backbone cable fails, the entire network gets disconnected
- as traffic increases, performance decreases
- low security as all computers on the network can see all data transmission
20
Q
STAR topology
A
- uses a central switch/computer to direct the flow of data
- MAC addresses identify each device
21
Q
Star topology advantages
A
- if one cable fails, only that computer/station is affected
- is more secure
- no data collisions as each station/device has its own cable to the server
- transmits data faster ( so better performance than bus topology)
22
Q
STAR topology disadvantages
A
- expensive to install due to switch and cabling
- maintaining the network is difficult because if the central device goes down, network data can no longer be transmitted to any of the nodes
23
Q
MESH topology
A
- every node is connected to every other node
- only one node requires a connection and all the others can share this connection
- most commonly found in wireless technology eg. WiFi
24
Q
MESH advantages
A
- no cabling costs as it is wireless
- the more nodes that are installed, the faster and more reliable the network becomes
- this is because if there is a break in any of the connections, traffic can be routed via another route
- new nodes are automatically incorporated into the network
- Faster communication since data packets don’t need to travel via a central switch
25
MESH disadvantages
- requires devices with wireless capabilities
- maintaining the network is difficult
26
INTERNET STRUCTURE
- Internet is a collection of interconnect networks (WAN)
- www is just a service of the internet
27
Protocol layering + benefits
- divides network protocols into layers each of which performs specific functions ( modular design ) [1]
- used to apply protocols in order/ one after the other [1]
- allows different layers to be worked on independently [1]
- allowed layers to be upgraded/updated without affecting others [1]
- allows for layers from different providers to be used interchangeably [1]
28
TCP/IP stack
- stands for Transmission Control Protocol / Internet protocol [1]
- TCP/IP is a set of rules used for communicating across a network [1]
- each protocol belongs to a different layer [1]
- consists of the following layers [1] :
- application layer
- transport layer
- internet layer
- link layer
- a set of networking protocols that work together as 4 connected layers passing incoming and outgoing data packets up and down the layers during network communication
29
Application layer
- based at the top of the stack
- protocol to be used is decided based on the application (used to transmit data) [1]
- e.g if the application being used to send the message was a web browser we could use HTTP/HTTPS , FTP [1]
- adds encryption if HTTPS is used [1]
- passes on data to transport layer for transmission [1]
- gets data from the transport layer when receiving [1]
30
Transport layer
- receives data/segments from the application layer
- uses the TCP to establish an end to end connection between the source and recipient computer
- splits up data into packets
- each packet is labelled with the:
- packet number
- port number
- total number of packets
- packets are numbered so the can be reassembled In the correct order
- if any packets go astray during the connection, the transport layer requests transmission of any lost packets
31
Internet layer
- receives packets from the transport layer
- adds the source and destination IP addresses
- this layer is responsible for routing each packet across the network using IP addresses
- all routers operate at this layer, the router uses the IP address to forward the packets
- IP address + port number = socket
- IP: the device the packet is being sent to
- port: application of the device that needs the packet
32
Link layer
- receives data from the internet layer to send [1]
- adds the unique MAC addresses to the packets [1] (identifying the NICS of the source and destination computers )
- passes layered data back up to internet layer when receiving [1]
Context :
- is the actual physical connection between network devices/nodes
- translates the digital packet into an electrical signal that can be sent over a network
33
What happens on the recipient computer ?
- the layers occur again in reverse
- link layer : removes MAC addresses
- internet layer : removes the IP addresses
- transport layer : removes the port number and reassembles the packets
- application layer : presents the data to the recipient in the format it was sent
34
IP address
- a numerical address made from 4 numbers each between 0 and 255 (IPv4) [1]
- which is a unique identifier for a device on a network [1]
- is a logical address/identifier [1]
- can be changed ( on a physical device )
- responsible for global identification
- indicates where a data packet is to be sent or has been sent from
- if a domain name is associated with an IP address, the IP address is the address of the server that the website resides on
35
MAC address (media access control)
- is a 6 byte unique hexadecimal address assigned to a NIC card used to identify a device
- MAC is the physical address of a computer and is hard coded into the device at manufacturing
- MAC address identifies network devices on a local scale
- MAC address are permanent, can’t be changed
- can’t be found by third party
36
Domain name
Is a unique human readable name that identifies a website on the internet and is associated an IP address on the internet
37
DNS ( domain name system )
- is the system used to name and organise internet resources
- translates the domain name into its associated IP address
- benefits : domain names are much easier to remember than IP addresses
38
URL ( uniform resource locater )
- is the full address of an internet resource
- specifies the :
- location of a resource on internet
- resource name
- file type
So that the browser can request it from the website server
39
Explain how the DNS plays a role in websites being loaded
- the DNS is used to associate IP addresses with URLs [1]
- the user web browser sends a request to the DNS resolver [1]
- the resolver checks its local cache for the URL
- if the resolver doesn’t have the URL, it forwards the request to the TLD name server [1]
- or if the Q is 3 marks : if the server doesn’t have the domain name/ URL it passes the request recursively to another DNS resolver [1]
- the TLD name server checks its cache for the URL
- if not found , the TLD name server directs the resolver to the authoritative name server for the specific domain
- the authoritative name server produces the IP address associated with the URL [1]
- the IP address is retuned to the DNS resolver [1]
- finally the DNS resolver sends the IP address back to the users browser or an error is communicated if no resolution can be found [1]
40
Why are IP address needed or useful?
- IP addresses can help identify a user [1]
- so companies can potentially track users attempting to gain unauthorised access [1]
41
LAN (Local area network)
- A network that covers a small Geographical area typically located on a single site [1]
- all infrastructure/hardware for LAN is owned by the network owner [1]
- this makes LANs more secure than WANs which have connections owned by 3rd part companies [1]
- LANs are typically connected using: UTP cable, fibre optic, WiFi
- example of LAN : home WiFi networks
42
LAN advantages
- users on the network can communicate with each other [1]
- users on the network can share peripheral devices/software/data [1]
- users on the network can share files [1]
- users in network can share internet connection [1]
- simplifies backup procedures/central backups [1]
43
LAN disadvantages
- access to data and peripherals can be slow if there is a lot of network traffic
- requires maintenance to ensure software is up to date
- upgrades back ups can be costly
44
WAN
- a wide area network that covers a large geographical area and often uses third party connections [1]
- is less secure than LAN [1]
- a collection of LANs eg. Connecting two LANs between 2 cities makes a WAN
45
Data packets
- Packets are units of data
- are small and easier to manage
- when a message is too large to be sent as a single unit, it is divided to smaller more manageable units called packets
46
Header
- Each packet is composed of a :
Header :
- includes sender and recipient IP address
- protocol being used
- order of packets ( for reassembling)
- packet length- size of the packet
- hop limit: tells packet when to expire and discard so that it does not travel forever
47
Payload
The actual data to be transmitted
48
Trailer
- signifies the end of the packet
- may also contain :
- checksum: a value used for error checking
- cyclical redundancy check to detect any transmission errors
49
Bandwidth
The maximum possible data transfer rate of a network
50
Packet switching
- a method of communication
- best for data that can tolerate some delay eg. Emails, webpages
- data is split into chunks called packets [1]
- each packet has a header which includes the address being sent to and order of the packet [1]
- each packet is sent is across the most efficient/optimum route [1]
- routes can vary for each packet [1]
- this means packets may arrive in a different order to which they were sent [1]
- once packets arrive at the receiver/final destination they are reordered [1]
51
Packet switching benefits
- transmission is safer from interception [1]
- because it is hard to intercept all the packets as they use different routes [1]
- very efficient use of network resources [1]
- as packets can follow different paths to the destination using more of the available bandwidth [1]
- is more robust against network failures as packets can be rerouted/retransmitted easily [1]
- meaning it is more reliable as if a single packet fails to reach its destination only that packet needs to be resent , not the entire data stream [1]
52
Packet switching CONS
- packets can arrive out of order, requiring reassembly of data packets and error checking
- must wait for all packets to arrive before data can be received so their can be delays
53
Circuit switching
- A method of communication
- where a direct link is created between two devices for the duration of the communication
- data is transmitted as a continuous stream
- Circuit switching requires the two devices to transfer and receive data at the same rate
- ideal for real time services like voice calls or video conferencing that require low latency
54
Circuit switching benefits
- data arrives in order as it follows the same path allowing for quicker reconstruction of the data
- enables two users to hold a call without delay in speech
- no delays as a dedicated path is established
55
circuit switching CONS
- bandwidth is wasted during periods of time in which no data is being sent
- devices must transfer and receive data at the same rate
- using switches mean electrical interference could be produced which can corrupt or destroy data
- ties up sections of the network which can’t be used by other data until transmission has been completed
56
NETWORK THREATS
- hackers
- viruses
- malware
- denial of service
- distributed denial of service
- SQL injection
- phishing
57
Hackers
Individuals or groups which exploit system vulnerabilities to gain unauthorised access to data, with malicious intent
58
Malware
Malicious software designed to harm or gain unauthorised access to a system or a network
Includes :
- worm
- virus
- Trojan horse
- spyware - records all key presses and transmits them to a third party
- ransomware - encrypts users files and demands for a ransom payment to decrypt them
59
DOS (denial of service)
Where a computer floods a server with useless traffic causing the server to become overloaded which causes it to crash or become unavailable to users
- often target web serves of big companies - banks, e-commerce businesses etc
- may cause damage to reputation
60
DDOS (distributed denial of service)
- occurs when multiple systems orchestrate a synchronised Dos attack against a single target
- instead of being attacked from one location, the target is attacked from many locations
61
SQL injection
- where malicious SQL statements are inserted in an entry field for execution
- can expose databases revealing private data
- data in databases can be amended or deleted
- new rogue records can be added to the database
62
Phishing
A type of fraudulent email which aims to steal sensitive info from users
63
Virus
- Malicious software that attaches itself to a legitimate program or file and then replicates itself to spread to other programs or files on the computer
- viruses may delete data/damage hardware
64
Worm
- is a standalone software that can replicate itself over networks without any user intervention
- unlike virus a worm can replicate itself and send copies to other users from your computer eg. By emailing
- worms are responsible for using up :
- bandwidth
- system memory
- network resources
- causing computers to slow down and servers to stop responding
65
Virus and worm comparison
- both have the ability to self replicate by spreading copies of themselves
- viruses rely on host files which are usually executable programs to be opened in order to spread themselves whereas worms don’t and can replicate on their own
66
Trojan
- a program that disguises itself as a legitimate program or file but when installed it can delete data or damage hardware
- Trojan can’t self replicate
67
types of NETWORK Protection
- firewall
- proxy server
- packet filtering/static filtering
- encryption
- antivirus software
- secure password
- regular software updates
68
Firewall
- a hardware device or a peice of software that monitors and filters traffic/packets going to and from a network [1]
- prevents unauthorised access to a network [1]
- used to protect companies data/intellectual property [1]
- used to restrict websites that can be accessed from within the company [1]
69
packet filtering/ static filtering
- limits network access in accordance with administrator rules and policies
- it works by examining the source and destination IP address aswell as the ports being requested and the protocols being used
- when access is denied by a firewall a packet can be either dropped or rejected
- rejected packet : sends an alert to the user to notify them of the error
- dropped packet does not
70
Proxy servers
- acts as an intermediary, collecting and sending data on behalf of the user
- the privacy of the user is protected and they remain anonymous
- the proxy server can cache frequently used website data making it faster to load
- proxies can reduce overall web traffic
- can be used by administrators to prevent access to sensitive or irrelevant info at work or at school
71
NETWORK hardware
- NIC
- switches
- WAPS
- routers
- gateways
72
NIC (network interface card)
- is required to connect a device to a network
- is usually built into hardware and assigns a unique MAC address to each device
73
Switch
- sends packets and receives packets [1]
- joins computers/devices together on a LAN
- Commonly used In star topology
74
WAPs (wireless access point)
- allow devices to connect to a network wirelessly
- most commonly used to connect devices to a router which can allow internet access
- used in mesh networks
75
Routers
- a device that passes data between two networks [1]
- is used to connect two or more networks together eg a LAN and a LAN or a WAN and a WAN
- a routing algorithm is used to find optimum route eg. Dijkstras algorithm
76
Gateways
- a device which connects two dissimilar networks together [1]
- are used when protocols aren’t the same between networks [1]
- translates protocols so that both networks can have the same protocols
- remove header data from packet before the remaining raw data is added with the new protocol of the new network in mind
77
Client server network model
- client computers connect to a server [1]
- server provides access to a resource/service [1]
- Use case : large organisations
78
Client server advantages
- central backups (in on location) eliminate the need for individual client backups [1]
- centrally administered in one location [1]
- Easier to keep data secure as files are stored in a central location and access rights are managed by the server [1]
- data and resources can be shared between clients
79
Client server disadvantages
- central/single point of failure ( if the server goes down services could become unavailable) [1]
- can be expensive to set up (require specialist staff to maintain network) [1]
80
Peer to peer network model
- there is no central server [1]
- devices on the network share data [1]
- a peer is a computer connected to the network
- use case: home networks
81
Peer to peer advantages
- no dependency on a central server
- is cheap to set up
- enables users to share resources such as printer, router etc
- is easier to maintain/ does not require specialist staff
82
Peer to peer disadvantages
- each machine is responsible for its own security and backups
- lack of central control can lead to security issues and vulnerabilities
