1.3.3 Networks - The Internet Flashcards
Internet
A network of interconnected devices
World Wide Web
A collection of resources accessible via the internet
Backbone
A set of dedicated connectors that connect several large networks at different points on the globe
Internet Protocol (IP) Address
A unique identifier for each device on a network, IPv4 has four 8-bit values separated by dots
Uniform Resource Locator (URL)
Specifies the means of accessing a resource across a network as well as its location
Handled by internet registries
Domain Name System (DNS)
The architecture used to map a URL to an IP address. Stored in a DNS server
Finding an IP address
Checked by the local DNS, the client’s known DNS server, the root DNS then the .co DNS until one can find the IP address
Protocol
The first part of a URL, usually https:
Host server name
The second part of a URL, the name of the server, often www.
Domain name and second domain name
The domain name is the name of the website e.g. ocr/bbc
The second domain name is usually the type e.g. .edu/.sch
Circuit Switching
Creating a communication connection between two endpoints for the duration of data transfer
Packets
The equal size chunks that data is broken down into and are received
Latency
The time taken for a packet to reach its endpoint
Transportation of Packets
Routers store data about available routes to neighbouring routers in a routing table. The router will send the packet to the nearest router that doesn’t go backwards, this is repeated to the end destination.
Hop
A transfer of packets between routers
Sequence number
Tells the receiver which order the packets should be in
What does a header contain?
The sender and recipient’s IP address, the protocol being used, the time to live (hop limit) and packet number x of y
What does a trailer contain?
The end of packet flag and checksum/CRC (cyclic redundancy checking). Used to check the data has not been corrupted.
Packet size
Typically 500-1500 bytes
Packets are small to ensure that packets don’t take too long to transfer but not too large that adding headers and trailers slows it down.
Protocol
A set of rules, or a formal description, of the format of digital transmission
TCP/IP and layers
Transmission control protocol / internet protocol
A stack, top to bottom: application, transport, network, link
Application layer
Defines what information is put together to send data and what protocol should be used, displays to the user on return
Transport layer
Splits the data into a series of packets and numbers each, requests retransmission of lost packets. Reorders packets upon receiving
Network layer
Addresses packets with the source and destination IP addresses, removes on return.
Link layer
Adds the MAC address of the source and destination or the router if across a different network, removes MAC address on return.
MAC address
Media Access Control - Uniquely identifies a physical device with a network interface card.
A 48-bit 12-digit hexadecimal number
Port number
Used to alert a specific application to deal with data sent to a computer, used by a protocol to specify what data is sent
FTP
File transfer protocol - An application level protocol used to move files across a network
Email protocols
Use SMTP to send, POP3 to download from a mail server and IMAP to manage emails on a server. POP3 is only on one computer, IMAP across multiple.
Firewall security uses
Only open certain ports so only certain traffic can enter
Packet filtering
Where the firewall inspects packets to see which port they are trying to enter
Proxy server
Makes a request on behalf of your computer, hides the request IP address from the recipient
Proxy server uses
Enables anonymous surfing, filters undesirable web content, logs user data with their request, produces a cache of previously visited sites
Botnets
A collection of software robots which infect unknowing computers
Distributed denial of service (DDoS)
Where a malicious user sabotages a network of infected computers to sabotage a website or server by sending many requests
Hacking
The process by which cyber criminals take over a computer
Malware
Software which infects the computer that it is being run on
Pharming
Redirecting a URL to send users to a malicious website
Phishing
Fake emails or text messages created to look like they are from a legitimate source
Ransomware
Malware which requires you to pay a ransom to bypass it. Lock screen malware prevents access, encryption malware stops you accessing data
Spam
Mass distribution of unsolicited messages
Spoofing
A website or email address designed to appear like a legitimate source
Spyware
Software which connects personal information without you knowing
Trojan Horses
A malicious program disguised as or embedded in legitimate software
Viruses
Malicious computer programs intended to infect you and your contacts
Wi-FI eavesdropping
Recording information communicated over an unsecure Wi-Fi network
Worm
A malicious program stored in memory which can self-replicate.
HTTP
Hypertext Text Transfer Protocol
SMTP
Simple Mixed Transfer Protocol
IMAP
Internet Messaging Access Protocol
Blagging
A type of attack in which the attacker creates a situation in which the user shares confidential information or performs actions that aren’t usually performed
Firewall
A device deigned to prevent unauthorised access to a network. Consists of two NICs between the user and the internet.
