Networks, internet, www, cybersec Flashcards
Purpose of a network
- To share and access data
- to store and share data
- to share physical reosurces
- to track access and implement security policies
- to communicate and collaborate
Network scopes
WAN(country), MAN(10km,city), LAN(1km,building/office), PAN(10m, bluetooth)
Topology
Ring - not used anymore, undirectional and biderectional
Star - Wired/wireless network w/a CENTRAL ACCESS POINT. more failsafe as break in connection only affects single device
Bus - A wired connection on ethernet backbone (used in QUB). Devices connected to bus through network access points. Needs terminators?
Mesh - Interconected (wired/unwired) between every computer. Failsafe as data can always be routed directly or indirectly
Bus vs star network
- Bus allows devices to DIRECTLY communicate
- Star allows INDIRECT communication through intermediary central machine (switch)
Examples of network devices
(with compatible characteristics)
Repeater - connects two buses, passes all signals back and forth
Bridge - two buses, only passes signals for other computers on the bus
Switch - acts like a bridge but connects multiple buses
(with incompatible characteristics)
Router - connects two incompatible networks resulting in a network of networks called an internet
Gateway - similar to router but connects a network to the outside world (the wider internet). includes satelite gateways
What is an IP address
- A unique address assigned to every device connected to the Internet
- 32 bit (IPv4), 128 bit(IPv6)
How do we look up websites
- Type in url
- Sent over the internet using http (protcol) to DNS SERVER
- Does DNS lookup, returns IP address
top-level domains and domain name example
.gov, .org, .com, .mil, .uk, www.google.com
People responsible for IP addresses
ICANN (Internet corporation for Assigned Names & Numbers)
- they allocate blocks of IP addresses to ISPs who then assign those addresses within their regions
Protocols
Protocols are rules by which activities are conducted on a network. for example, http.
OSI 7 layer model
7 - Application layer - human computer interaction layer
6 - Presentation layer - ensures the data is in a usable format, where data encryption occurs
5 - Session layer - Maintains connections and is responsible for controlling ports and sessions
4 - transport layer - transmits data using transmission protocols including TCP and UDP
3 - Network layer - decides which physical path the data will take
2 - Datalink layer - defines format of data on the network
1 - Physical layer - transmits raw bit stream over physical medium
OSI acronym
Open systems interconnection model (bottom up)
Please
Do
Not
Throw
Sausage
Pizza
Away
Internet protocols
At application layer (highest layer) ** contains transfer
HTTP - Hypertext transfer protocol
FTP - File transfer protocol
SMTP - Simple mail transfer protocol
NNTP - Network news transfer protocol
At transport layer (important) ** does not contain transfer
TCP/IP - Transmission control protocol/Internet protocol
UDP - User datagram protocol
What does the transport layer do?
Handles end-to-end connections
TCP and UDP protocols package data into small packets to be sent onto another device
TCP
Transmission control protocol
Before a message is sent between client and server there is request, acknowledgement, acknowledgement
known as three-way handshake
Difference between TCP and UDP packet
TCP uses threeway handshake, UDP does not. Problem with this is packets can arrive in wrong order.
TCP is slower but reliable. Used in email and web browsing.
UDP is faster but unreliable. Used in VoIP and music streaming.
** remember T in TCP for three way handshake
Difference between TCP and UDP packet
TCP uses threeway handshake, UDP does not. Problem with this is packets can arrive in wrong order.
URL
Uniform resource locator
protocol://host.address/directoryPath/documentName
What does HTML do?
Hypertext markup language
HTML tags describe
- How it displays
- Links to multimedia files
- links to other documents
connect a network to outside world
gateway
A simple web page in html
Tag indicating beginning of document - html
Preliminaries - head and title
diplayed on webpage - body
end of document - html
beginning and end <> and </>
