Communications and Network Security Flashcards
What does OSI stand for?
Open Systems Interconnection - created by ISO (International standard for organisation)
What is the most widely used protocol?
TCP/IP protocol (based on TCP/IP model)
Explain a protocol?
A protocol is the way in which two computers are able to communication over a network (think of it like a path between houses)
What is the main goal of the OSI?
To support data exchange and network communications. Also to ensure different products can communicate across vendors - i.e CISCO switch can communicate with netgear router.
Name the Seven layers of the OSI?
All People Seem To Need Domino’s Pizza
What moves across the physical wire?
Electrons over copper
Photons over fiber
Radio signals through the air (wifi)
What part of the OSI model does each layer communicate with?
Up, down and to it’s peer layer (for authentication)
Explain encapsulation/descaps
Employed by protocols
The addition of a header or footer to direct the data
They combine to become the payload
They contain instructions so the peer layers can communicate
At what point is the message converted into electrical impulses that represent bits?
In the physical layer so that it can be transferred over the wire
What does the physical layer do when it receives the message?
converts the message into bits. Before converting it to frames at the data link layer
Name the different types of message at each layer?
Data (session, presentation, application) Segement/datagram (transport layer) packet (network layer) Frame (data link layer) Bits (physical)
The message in a network is a segment when?
It uses TCP protocols
The message in a network is a datagram when?
It uses UDP protocols
What are the two networking model and which one do all networks use?
OSI and TCP/IP - all networks support TCP/IP stack but OSI is used as a benchmark.
They are standards on how systems are built and networks communicate. It means we can all talk together and use the same protocols etc.
Name the layers of the TCP/IP model?
All twats need domino’s pizza
What layer does a hub operate at?
Hubs operate at layer 1 because they are simple and stupid - they only repeat electric signals. Similar to a repeater on layer 1 too.
What is the first thing that Ron must do before he tried to buy coffee off Starbucks?
- Send out ARP request for DNS server and then send out a DNS request to get the IP address of website
- Do the same for the router so that he can go outside
- then send the message to the switch > router > switch > Web server
What happens at the application level?
You attempt to access a website for example, or attempt to send an email. They are protocols used by web browsers for example. Includes HTTPs/
What happens at layer 4 (transport layer)?
This is where you outline and add headers that describe how you are going to send the data and which ports you are going to use - i.e HTTPS and port 443 - so that the other layers know
When your browser tries to access a website and it adds a HTTP header to the data - what is this called?
Encapsulation
Each layer adds a header to the data/segment/frame/packets/bits - what is this called?
Encapsulation
What is the benefit of adding layer 3 headings?
It add’s destination and source IP addresses and tells the router where to direct the message (this message is a packet)
What is the benefit of adding layer 2 headings?
It gives instructions to our switch (this message is a frame) - where to send the message
Once you encapsulate the data and send your message - what type of message does the switch (on your side) receive at layer 2?
It receives a frame, which only contains the MAC address data (the rest is encapsulated and can’t be read). The Switch see’s this information by decapsulating the message and uses the MAC address to forward on the message.
This will typically be the MAC address of the router, as it needs to be send outside the network.
How does the router learn the IP address of a website?
It does this through ARP - and then encapsulates this information into a new mac address header and footer. The original footer would have contained IP/MAC adderesses of the sender and router.
What happens when the server receives the frame from a switch?
It can read all the layers and it checks each one to make sure it contains his/her MAC address, IP address, and see’s that it’s using TCP on port 443 (for example). It then passes it up to the application level and it can see that it’s HTTP and for the browser.
What are the two protocols that you can choose when using the transport layer?
TCP, UDP