Unit 5 - Networking Flashcards
what is a router
a router allows us to forward data packets across the network using the same protocol
what is a server
a server is a computer or system that provides resources, data, services, or programs to other computers, known as clients, over a network.
what is a switch
it receives data packets, inspects the packet for who the intended recipient is and then sends it onto the correct client.
what is a hub
it receives a data packet and then sends it to the all the clients in the network, who then have to determine if it’s for them
what is a wap
wireless access point - a device that creates a wireless LAN and usually connects to a router for internet
what is a NIC
network interface card - adds an additional communication port on a device to allow it be connected to a network
what is a bridge
connects two networks that use the same protocol
what is a gateway
routes data packets across two dissimilar networks (different protocols)
what is a modem
modulated demodulator - converts a digital signal to an analogue one so it can send data down a telephone line
define WAN
wide area network - over a geographically dispersed area and uses third-party infrastructure, such as an internet service provider
define world wide web
a collection of resources that can be accessed via the internet
define internet
a collection of inter-connected networks
define an FTP client
when you can send something across the internet without using the WWW
what is the structure of the internet
- backbone - a set of dedicated connections that connect several large networks at various points on the globe
- each of these points are then connected to other regional networks
- an ISP provides individual access to end-users
what is an internet address and what is it made out of
- each device on a network needs to be uniquely identifies so that data can be sent to the correct destination
combines: - MAC address - assigned to a device through the NIC
- IP address - identifies the router
format of IPv4
4 octets = xxx.xxx.xxx.xxx
format of IPv6
6 octets = xxx.xxx.xxx.xxx.xxx.xxx
what is a url
uniform resource locator - full address of an internet resource. it specifies the means of accessing a resource across a network and its location
combines:
- protocol
- domain name
what is a DNS
domain name system - dedicated computers with an index of domain names and their corresponding IP addresses
how does a DNS work/ what is its structure
when a computer queries a DNS server of a domain name, the server returns an IP address that the computer can use to send a message. when the IP address of a given domain is not known it is referred to a related domain server that they may know
structure:
- 13 root DNS servers
- segmented into geographical levels
how to resolve an IP address
suppose that a client has no cached record of an IP address:
- if the DNS server does not have a record for that domain it:
1. either recursively handles the request so that it can eventually deliver an IP address
2. or refers to the DNS server authoritative and follows this, and subsequent referrals, to successively lower-level DNS servers
what is a proxy server
acts on your behalf, protects the details of your client server from the outside world when doing tasks such as sending requests on the web
what is an SAN
storage area network - secondary storage devices connected in a raid formation
what is a PAN
personal area network - within a few meters, generally connected via Bluetooth
what is a metro network
network in a metropolitan area, ring around the city
what is a trunk network
connects countries and cities
what is a LAN
local area network - over a geographically concentrated area and uses first party infrastructure
what is a network topology
the arrangement of various computing devices which make up a computer network
structure of a bus topology
an arrangement where nodes are connected in a daisy chain by a single central communication channel
operation of a bus topology
- all nodes connected via a single backbone
- each end of the backbone is connected to either a terminator or a computer which stops signals ‘bouncing back’
- each node is passive
- data is sent in one direction at a time only
- only one computer can transmit successfully at one time
advantages of a bus topology
- inexpensive to set up
- devices can be easily added
- good for small networks
disadvantages of a bus topology
- main cable is a point of failure
- limited cable length
- performance degrades with heavy use, leading to data collisions
- poor security
what is a star topology
an arragement where a central node, switch or hub provides a common connection point for all other nodes
operation of a star topology
the central switch keeps a record on the unique MAC address of each device on the network and can identify which particular computer on the network it should send the data to
what is a physical topology
a network defines how the devices are physically connected, uses hardware
what is a logical topology
how the devices communicate across the physical topologies, uses software
define circuit switching
a direct end-to-end connection between two devices which means that only those two devices with that connection can communicate data any given time
what is a data packet and how are they used
- data is broken into chunks (units) called data packets and assembled again at the receiving end (increases network efficiency & reliability)
- they are assigned a TTL (time to live), if a receipt for a data packet isn’t received by the sender before the TTL runs out, the data packet is sent again
- the delay between sending and receiving data packets is called latency
what is packet switching
packets are often sent across networks that have multiple connections with multiple routes through a destination – these networks are also often shared. each packet takes the fastest available route.
what is routing packets and how does it work
routers forward data packets from one network to another:
- each router stores data about the available routes to the destination node
- looks up the destination IP address in its routing table to find the best router to forward the packet to
- each transfer between routers is known as a hop
- routers continue to forward the packet until it reaches its destination node
how are packets made
TRAILER – end of packet flag, error checking components, checksum or cyclical redundancy checks (CRCs)
payload – data
HEADER – sender’s IP address, recipient’s IP address, protocol, packet number x of y, TTL or hop limit
describe the reason for small packet size
to ensure that individual packets do not take excessive time to transfer preventing other packets from moving.
- however, they should, not be too small as the additional data added makes data transfer inefficient as unnecessary headers and trailer would be required each time.
define protocol
a set of rules, or formal description, of the format of digital transmission
steps to error check a barcode/packet
- write out the barcode and ignore the last number(check digit)
- from the right hand side add up the total of every alternate digit
- multiply that total by three
- from the right hand side add up the alternate numbers that have not been used
- add both of the totals together
- work out how much should be added on to reach the nearest ten – this should be the check digit
what does a protocol cover
- size of packets
- contents & format of header
- error detection & correction procedure
why are gateways needed
required where data is travelling from one network to another that uses different protocols
- networks using different transmission media
- header data is removed and re-applied using the correct format
what is the TCP/IP protocol stack
a set of rules used in turn, to format a message so it can be sent over a network. each layer wraps the packets with its own header data.
what is the order of layers for a packet being sent in the tcp/ip protocol stack
application
transport
internet
link
what is the order of layers for a packet being received in the tcp/ip protocol stack
link
internet
transport
application
what happens in the application layer when sending a packet
- uses high-level protocols that set up an agreed standard between the communicating end-point
e.g. = SMTP, FTP, HTTP - does not determine how the data is transmitted, rather specifies the rules of what should be sent
what does the transport layer do when sending a packet
- uses TCP (transmission control protocol) to establish an end-to-end connection with the recipient user
- splits data into packets & numbers them sequentially
- adds port number to be used based on HTTP protocol
what does the internet layer do when sending a packet
- uses the IP (internet protocol) to address packets with the source and destination addresses
what does the link layer do when sending a packet
- operates across a physical connection
- adds the MAC address of the physical NIC that packets should be sent to based in the IP address
- MAC addresses change with each hop
what does the link layer do when receiving data
removes MAC and passes to the internet layer
what does the internet layer do when receiving data
removes IP and passes to transport layer
what does the transport layer do when receiving data
removes the port number from each packet, reassembles the packets in the correct order and passes to the application layer
what does the application layer do when receiving data
presents the image data for the user in a browser
what is a MAC address
media access control - uniquely identifies a physical device with a NIC
- this may be the destination computer or router in transit
- packets move up and down the lower layers of the stack as they hop across routers, changing their source and destination MAC addresses as they go
what is a port number and what is it used for
- a port is used to alert a specific application to deal with data sent to a computer
- used by protocols to specify what data is being sent
what is FTP and what is it used for
file transfer protocol - uses the client-server model with separate data and control channels. access can be provided anonymously where any user can access the FTP site
what is SMTP and what is it used for
simple mail transfer protocol - used to send emails and forward them between mail servers to find their destination
what is POP3 and what is it used for
downloads the email stored on a remote server to a local client (removed after download)
what is IMAP and what is it used for
Manages emails on a server so multiple clients can access the same email account in synchronicity
what is a firewall
either software or hardware that controls access to and from a network. numbered doors called ports are opened so that only certain traffic is allowed to pass through.
how are firewalls used
PACKET FILTERING:
- packets of data are inspected by the firewall to check which port they are attempting to access. different network protocols use different port numbers. if this traffic is allowed through, the port must be opened for the duration of connection, otherwise the firewall will automatically reject it.
what is a proxy server used for
makes a web request on behalf of your own computer, hiding the true request IP addresses from the recipient.
what are some functions of a proxy server
- enables anonymous surfing
- can be used to filter undesirable online content
- logs user data with their requests
- provides a cache of previously visited sites to speed across
what is the main difference between a VPN and a proxy server
VPN - encrypts messages (proxy does not)
what is encryption
the act of encoding a plaintext message so that it cannot be deciphered unless you have a numerical key to decrypt.
why is encryption used
- if the message is intercepted it cannot be understand
- if the key can be intercepted, the encryption is rendered useless.
why does code quality increase network security
improving code quality, together with monitoring attempts to gain unauthorised access and protection can significantly reduce threats from malware.
Include:
- guarding against buffer overflow attacks
- guarding against SQL injection attack
- use of strong passwords for login credentials
- two-factor authentication
- use of access rights
why does monitoring increase network security
can protect against the threat of hacking, which can introduce malware. these can be used to protect against the threat of malware and hacking, in particular, packet sniffing and user access logs.
why does prevention increase network security
- up-to-date patches to the operating system and application programs reduce vulnerabilities in the system
- up-to-date anti-malware (“anti-virus”) software can prevent the spread of infection
define malware
annoys users or damages their data
what is a virus
a virus infects (embeds itself in) other programs or data files, a virus needs a user (a host) to help it spread.
what is a worm and what does it do
a standalone program that does not require a user to run it in order for it to spread (self-replicates). worms exploit vulnerabilities in the destination system and spreads automatically.
- generally, slow the system down.
what is a trojan and what does it do
malicious software programs that masquerade as innocuous or useful applications.
- they cannot self –replicate
- often they serve to open up back doors in your computer to the Internet so that the processing power, Internet bandwidth and data can be exploited remotely.
what is phishing and how is it used
SOCIAL ENGINEERING
- phishing is using email to manipulate a victim into visiting a fake website and giving away personal information.
what is a buffer overflow and how does it work
when a program accidentally writes data to a location too small to handle it. as a result the overflowed data may end up in a neighbouring instruction space. malware can deliberately cause and manipulate overflow data which may then be read as a malicious instruction.
what is an sql injection and how does it work
ONLY IN WEB FORMS
- a malicious user can enter SQL commands via online database forms to change the processing.
define html
hypertext markup language - language/script web pages are written in. describes the content and structure of a web page
- used with css
what is the difference between html and css
html - defines page content and structure
CSS - defines page style and appearance
what are the sections of a webpage
- head = page metadata
- body = page content
what does the <title> tag define</title>
tab heading
what does the <p> tag define
- define new blocks of content
- new line for new content within them
how to define a list in html
<ol> = numberd list
<ul> = bullet points
<li> = new line in list
</li></ul></ol>
what does an <a> tag define</a>
anchor tag - defining a hyperlink with location parameter
what does an <img></img> tag define
self closing image tag
what does the <div> tag define
division of the page into seperate areas, which can be styled differently using CSS
what does css stand for
cascading syle sheet
how can css be inserted into a HTML doc
- internal or embedded css between tags <style> in the head section</style>
- external style sheet with <link></link> tags
what does a css identifier do
- defined with #
- unique to every webpage
- you can hang styles
what does a css class do
- use . as prefix
- can be used multiple times on a webpage
- hang styles
what are web forms
- enable websites to collect user input data and selections
- can be validated using javascript
- use HTML <form> tags
example of how a web form could be written
<form action=”…” method=”post” enctype=”text/plain”
Name: <input></input><br></br><br></br>
Message: <textarea>
</textarea><br></br><br></br>
<input type = “submit” value = “submit”
</form>
what is javascript
- programming language similar to python & VB
- adds interactivity to websites
- interpreted = needs to be translated into object code for whichever computer there browser is running on
why is javascript used for validation of inputs
- local computer can validate erroneous data before submission to a database
- a busy server is relieved from having to process everything itself
name some features of javascript
- drawing and animations
- manipulation of HTML elements such as text and images
- navigation tools such as tabs and accordions
- web form validation before transmission
what code structures does javascript use
- variables
- functions
- conditionals
- loops
- arrays
advantages of an external js script file rather than direct embedding
- code cleaner and easier to read
- can be linked to multiple html files
- changes to a single external file can affect multiple html files
code to create a variable in javascript
var x = document.getElementById(“Box”)
code for functions in javascript
<script>
function myFunction() {
var x = … ;
x.style.fontSize = ...;
x.style.color = …;
}
</script>calling functions in javascript
button action:
onclick = “myFunction()”
code to ouput something in javascript
<script>
document.write("…")
</script>code for arrays in javascript
var arrayName = [“a”, “b”, “c”]
what is a search engine
systems that locate resources on the world wide web
what is search engine indexing
- search engines keep a record of the resources located on the World Wide Web
- known as an index
- the process of creating an index includes using a piece of software called a web crawler or spiders
what is a web crawler
- internet bots that continuously crawl the web to discover and record publicly available web pages.
- web crawlers look at web pages and follow the hyperlinks located on those pages
- the web crawler then continues to follow the hyperlinks on the proceeding pages
- it does for billions of web pages. the web crawler keeps a record known as the index.
examples of information web crawlers sort their index by
- the URL of the resource
- the content of the resource
- the last time the resource was updated
- the quality of the resource
what are meta tags
describe the content of the page. web developers can place meta tags inside HTML pages to make the page more likely to be found. hidden from users but discoverable by web crawlers.
what happens when we search the web
- web crawler searches the web, locating resources
- resource data copied to the index
- index is searched for relevant content
- search results returned
what is google’s page rank algorithm
- algorithm takes into account inbound links to a website to determine how useful page is
PR(A) = (1-d) + d (PR(Ti)/C(Ti) + … + PR(Tn)/C(Tn))
what does PR(A) stand for in the pagerank algorithm
the PageRank of page A – defined by the PageRank of page A is defined by the PageRanks of those pages linked to age
what does PR(Ti) stand for in the pagerank algorithm
the PageRank of pages Ti which link to page A (start by assuming it is 1)
what does d stand for in the pagerank algorithm
d is the damping factor (start by assuming that it is 0.85) - the probability of a random web browser reaching a page. OR (1-d) = the probability of r random web browser NOT reaching a page
what does C(Ti) stand for in the pagerank algorithm
C(Ti) is the number of outbound links on page Ti
factors taken in by search results ranking algorithms
- domain name – relevance to search item
- frequency of search term
- age
- frequency of page updates
- magnitude – of content updates
- keywords – in <h1> tags
what does a higher page rank value mean
the more relevant the page, in theory, and therefore the higher the page will appear on search results
what is the stucture of a client-server network
consits of two parts: client & server
1. client – accesses data, services and files from the server
- initiates communication to the server
2. server – waits for requests from clients
features of a client-server network
- a central server is used to manage security
- some files are held on the central server
- some processing tasks are performed by the server
- clients issue requests to the server for services such as email, file storage, backup and priniting
- suitable for many different types of organisations, small and large
- can require specialist IT staff to administer the network
features of a peer-to-peer network
- they are suitable for a small company or home network with a few computers
- no central server controls files or security
- all computers can see files on all other computers
- all computers can communicate with each other without going through a server
- if a computer is switched off, data cannot be retrieved from it
adv & dis of of client-server network
ADV:
- access levels centrally controlled
- backup is centralised and usually automated
- no access to other users’ files
- data and other resources can be shared
DIS:
- can be expensive to set up and manage
- IT staff needed
adv & dis of peer-to-peer network
ADV:
- files and programs stored on individual computers
- suitable for home networks
- cheap to set up and maintain
- each computer on the network can act as client or server
DIS:
- piracy as files are decentralised
what is client side processing
- data is processed before it is sent to a server by the client
- usually happens in the form of scripts and these are usually executed by the client browser
- web page does not communicate with the server
- javascript = client-side
advantages of client-side processing
- allows for more interactivity by immediate response
- quick execution as no communication with the server is required
- removes potentially unnecessary processing from the server
- data cannot be intercepted on the way to the server
disadvantages of client side processing
- not all browsers support all scripts
- dependent on the performance of the clients’ machine
- different browsers process scripts in different ways - lack of certainty of end-product
what is server side processing
- process data on behalf of multiple clients
- SQL and PHP
- Python and ASP
features and examples of client-side processing
- initial data validation
- procides web interactivity
- manipulates user interface elements
- applies styles - CSS
- reduces load on the server
- reduces the amount of web traffic
features and examples of server side processing
- provides further validation
- used to query a database
- updates server databases
- performs complex calculations
- encodes data to readable HTML
- keeps organisational data secure
what is an API
application programming interface - a set of tools that can be used for building software applications.
- requests are processed by the client and responded to by the relevant server.
what does the ‘thickness’ of a client mean
the level of processing and storage that it does compared with the server it is connected to
- thinner = more processing and storage done by server
adv of thin client
- easy to set up, maintain and add terminals to a network with little installation required locally
- software and updates can be installed on the server and automatically distributed to each client terminal
- more secure since data is all kept centrally in one place
disadvantages of thin client
- reliant on the server, if the server goes down, the terminals lose functionality
- requires a very powerful and reliable server which is expensive
- server demand and bandwidth increase
- maintaining network connections for portable devices consumes more battery power than local data processing
advantages of thick client
- robust and reliable, providing greater up-time
- can operate without a continuous connection to the server
- generally better for running more powerful software applications
disadvantages of thick client
- more expensive, higher specification client computers required
- installation of software required on each terminal separately and network administration time is increased
- integrity issues with distributed data
