Networks (Unit 5) (Finished) Flashcards
(5.1) What is the largest network in the world?
WWW (world wide web)
(5.1) What is an IP?
Internet protocol- defines a system with a unique number
(5.1) What is a MAC address?
Hard coded hexadecimal number that defines a system permanently
(5.1) What is a URL?
used to specify the means of accessing a resource across a network and its location
(5.1) What is DNS (domain name system?)
dedicated computers with a list of domain names and their corresponding IP addresses
(5.1) What is the structure of DNS servers?
Several global servers that work together to catalogue every website
(5.1) What is a backbone?
A set of dedicated, high transmission rate network connections between 2 geographical locations
(5.1) What is a LAN?
Local area network, two or more computers together within a small geographical area
(5.1) What components are needed for a wireless network?
Wireless Network Interface Card (NIC)
Wireless Access Point (WAP) requires a connection to a router, and the router requires a connection to a modem
(5.2) What is circuit switching?
creates a communication connection between 2 endpoints for a transfer of data
(5.2) What is a data packet?
Data is broken into chunks called packets and reassembled at the end
(5.2) What is time of travel known as
Latency
(5.2) What is packet switching?
when packets switch network routes in order to take the quickest possible route
(5.2) What is routing?
when routers create the optimal path for packets to travel along in order to get to their destination
(5.2) What is a data packet made up of?
trailer- end of packet
payload- data
header- holds ip addresses and packet number
(5.2) How big are packets?
Packets are deliberately small so that they don’t take excessive time moving
(5.2) What is the purpose of the packet header?
The header contains the recipient’s address so that it can be directed appropriately across the network
The address of the sender is also included so that replies can be sent appropriately
The packet number and overall number of packets in the transmission is attached to assist in reassembling the data
(5.2) What is the purpose of the packet trailer?
contains error checking
cycle redundancy is used to check the data by the receiving host
(5.2) What is a protocol?
A set of rules for data communication
(5.2) why are protocols important?
Protocols are important as the help enforce the rules of data communication
these protocols must be standard across all devices
(5.2) What are the protocols used in networks?
TCP/IP-Used to ensure data goes to the correct place on a network
DNS-Used to convert URLs to IP addresses
TLS/SSL-Encryption of data (not on the spec.)
HTTP/HTTPS-Viewing webpages (not on the spec.)
SMTP-Emailing (not on the spec.)
POP-Emailing (not on the spec.)
IMAP-Emailing (not on the spec.)
FTP/SFTP-Transferring files (not on the spec.)
Telnet-Old method of connecting to other terminals (not on the spec.)
(5.2) What is the TCP/IP stack?
The TCP/IP stack is a set of rules used in turn, to format a message so it can be sent over a network
Each layer provides a specific function within the transmission of the message
(5.2) What are the 4 layers of the TCP/IP stack?
Application Transport Internet (network) Link (A til)
(5.2) What happens in the application layer of the TCP/IP stack?
Used to provide services for applications that want to communicate across a network, often the Internet
Uses high-level protocols that set an agreed standard between the communicating end-points
For example, SMTP (for e-mail), FTP (for file transfer) and HTTP (for web browsing)
(5.2) What happens in the transport layer of the TCP/IP stack?
Uses the Transmission Control Protocol (TCP) to establish an end‐to‐end connection with the recipient computer
Splits data into packets and numbers them sequentially
Adds port number to be used based on HTTP protocol
At the receiving end this layer confirms that packets have been received and requests any missing packets be resent
(5.2) What happens in the internet layer of the TCP/IP stack?
Uses the Internet Protocol (IP) to address packets with the source and destination IP addresses
A router forwards each packet towards an endpoint called a socket, defined by the combination of IP address and port number: 42.205.110.140:80
Each router uses a routing table to instruct the next hop
(5.2) What happens in the link layer of the TCP/IP stack?
The link layer operates across a physical connection
Adds the MAC address of the physical NIC that packets should be sent to based on the destination IP address
MAC addresses change with each hop
(5.2) How is the data received in the TCP/IP stack?
At the destination, the message is passed back up through the layers
The Link Layer removes the MAC address from each packet and passes it to the internet Layer
The Internet Layer removes the IP address from each packet and passes it to the Transport Layer
The Transport Layer removes the port number from each packet, reassembles the packets in the correct order and passes them to the Application Layer
The Application Layer presents the image data for the user in a browser
(5.2) What is a MAC address?
A MAC address uniquely identifies a physical device with a Network Interface Card (NIC)
(5.2) What is a gateway, and what is it used for?
A computer that sits between different networks or applications
A gateway is required where data is travelling from one network to another that use different protocols
(5.2) What is a bridge?
can be used to connect Local area networks together.
(5.2) What is a hub?
is used to connect devices in a LAN
(5.2) What is a switch?
used to segment sections of a LAN
(5.2) What is a router?
used to connect to the internet – enables routing onto the internet
(5.2) What are the 3 protocols used for sending emails?
SMTP-Used to send emails and forward them between mail servers to their destination
POP3-Downloads email stored on a remote server to a local client (removed after download)
IMAP-Manages emails on a server so multiple clients can access the same email account in synchronicity
(5.2) What is the difference between IMAP and POP?
IMAP holds mail on the server so that multiple devices can access all mail
POP downloads mail to a local device and removes it from the server
(5.3) What is a firewall?
A firewall is either software or hardware that controls access to and from a network
(5.3) How are things allowed through a firewall?
Numbered doors called ports are opened so that only certain traffic is allowed to pass through
(5.3) What is packet filtering?
Packets of data are inspected by the firewall to check which port they are attempting to access
If this traffic is to be allowed through, the port must be opened for the duration of the connection, otherwise the firewall will automatically reject it.
(5.3) What is a proxy server?
a server that makes a web request on behalf of your own computer
(5.3) What are the functions of a proxy server?
Enables anonymous surfing
Can be used to filter undesirable online content
Can be used to disguise your location so you can access content you aren’t normally able to. (Foreign Netflix for instance)
Provides a cache of previously visited sites to speed access
(5.3) What is malicious software?
software intentionally designed to cause disruption and problems
Some examples include:
malware- annoy users + damage data
worms- self replicate
viruses- self replicates, infects itself into other programs, but needs a user to help it spread
(5.3) What are some measures that can be taken against malicious software?
Improving code quality careful monitoring Strong passwords 2 factor authentication guarding against SQL injection attack and buffer overflow attack
(5.3) What is buffer overflow?
When a program accidentally writes data to a location too small to handle it, which results in overflow data
(5.3) What is an SQL injection?
When a malicious user enters SQL commands via an online database to change the processing
(5.3) What is monitoring, and what are some methods of monitoring?
monitoring can protect against the threat of hacking, which can introduce malware
Some examples of this includes:
Packet sniffers
User access logs
File auditing q
(5.3) How can being up to date in updates be helpful in preventing hacking?
up to date patches to the software system helps to reduce vulnerabilities as new, more secure versions are constantly developed
(5.4) What is HTML?
Hyper Text Markup Language- the language of the world wide web
describes the content of web pages
(5.4) Where is HTML code stored?
Stored in a text file containing the contents of the website (such as text and images)
HTML uses tags to decide how to present sections of content
(5.4) What is the difference between CSS and HTML?
HTML is used to define the page content and structure
CSS are used to define page style and appearance
(5.4) What are the important HTML tags?
<h1> </h1>
<h2>
<img></img><a><div><p></p><li><ul></ul><ol>
</ol>
</li></div></a></h2>
(5.4) What are ordered lists?
A numbered list can be created using the <ol> tags</ol>
(5.4) What is an unordered list?
A bulleted list can be created using the <ul> tags</ul>
(5.4) How can you apply CSS styles?
Inline styling to apply a unique style within an HTML element
Internal, embedded styles defined within tags in the section of a single HTML file
Using an external style sheet and linking to it from any HTML files that may be created for an entire website
(5.4) How are external CSS files used?
External CSS files enable you to apply styles on a single CSS stylesheet to multiple HTML files throughout an entire website
(5.4) What does linking to an external CSS file do
Linked to an external CSS file will apply the same styles to any HTML files that link to it
(5.4) How are CSS style attributes linked to HTML sectors?
CSS style attributes are linked to HTML selectors
(5.5) why is JavaScript important?
One of the 3 essential web technologies
Can be used to:
Program behavior of web pages
add interactivity between the user and a web page
(5.5) What are the main 3 different programs of web design, and what are they mainly used for?
HTML is for adding content to a webpage/website.
CSS is for making a webpage/website look pretty.
JavaScript is for making a website interactive.
(5.5) What is meant by JavaScript being an interpreted language?
Web features are easier to implement and:
allow complex tasks to be performed relatively easily
can execute ‘on the fly’ – does not need to compile which makes it quicker to run
enable quick addition of interactive elements to web pages
can run on many devices
(5.5) What are the key components of JavaScript code?
Variables: assign, re-assign, and local vs. global scope
Functions: group code into functions, pass arguments to them, and return values from them
Conditionals: if/else statements and logical expressions
Loops: while and for loops to repeat code
Arrays: storing multiple pieces of data under a single variable
(5.5) How is JavaScript used in relation to HTML?
Like CSS, JavaScript can be added directly into a HTML file or written in external files and then linked to an HTML page
(5.5) How does Java deal with inputs?
JavaScript is commonly used to process data on the user’s machine as it is entered
This may validate data, animate objects/images such as shopping cart or provide other interactivity
(5.6) What is search engine indexing?
Search engines keep a record of the resources located on the World Wide Web
This is known as an index
(5.6) How are indexes generally created?
The process of creating an index includes using a piece of software called a web crawler or spider
(5.6) What is a web crawler, and what do they store?
Web crawlers are Internet bots that continuously crawl the web to discover and record publicly available web pages
Store:
The URL of the resource
The content of the resource (ie. Text on a web page)
The last time the resource was updated
The quality of the resource (ie. How credible it is)
(5.6) What is a meta tag?
Meta tags describe the content of a web page
(5.6) What is PageRank?
PageRank was developed to list search results in the order and rank of usefulness and relevance
The algorithms takes into account inbound links (links from other websites) to a website to determine how useful a web page is
The PageRank of page A is defined by the PageRanks of those pages linked to page A
(5.6) What are the key features of the PageRank algorithm? PR(A) = (1-d) + d (PR(Ti)/C(Ti) + … + PR(Tn)/C(Tn))
PR(A) is the PageRank of page A
PR(Ti) is the PageRank of pages Ti which link to page A
d is the damping factor (0.85)
C(Ti) is the number of outbound links on page Ti
(5.6) What are some factors that affect PageRank?
Domain name – relevance to the search item Frequency of search term in web page Age of web page Frequency of page updates Magnitude of content updates Keywords in <h1> tags </h1>
(5.7) What is validation?
Validation is used to see if the information that has been entered meets certain criteria before it is checked
(5.7) What is a client-server network model?
This network model consists of two parts: the client and the server
The client accesses data, services and files from the server
The client initiates communication to the server
The server waits for requests from clients
(5.7) What is an example of somewhere that would use a client-server model?
A school
(5.7) What are some features of a client server model?
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 printing
Suitable for many different types of organisation, small and large
Can require specialist IT staff to administer the network
(5.7) What is a peer-to-peer network?
a group of computers are linked together with equal permissions and responsibilities for processing data.
(5.7) What are some 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
(5.7) What is client processing?
Data is processed before it is sent to a server by the client
(5.7) What are the advantages and disadvantages of client processing?
Advantages:
Allows for more interactivity by immediately responding to a users’ action
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, increasing security for the user
Disadvantages:
Not all browsers support all scripts (although most modern browsers support an overwhelming majority)
Because the scripts are processed by the client, they are dependent on the performance of the clients’ machine
Different browsers process scripts in slightly different ways, so the web page owner cannot be certain how the end-product will look to the user
(5.7) What is Client side processing?
A client-side script is a program that is processed within the client browser.
(5.7) What is server side processing?
When the server:
Process user input – providing another layer of validation
Display pages
Structure web applications
Interact with permanent storage/databases using SQL
This is done in languages such as Python
(5.7) What are some advantages of server side processing?
The client does not always have the capability to provide the data required to successfully process a request
A company may hold sensitive data relating to the request
Server side is more secure as you cant see the code behind the process
The way the data is processed may also be a company secret and be protected by law
