A108 Computer Networks Flashcards
What does ISP stand for?
Internet Service Provider
What is a packet and what are the main items in the item header?
A packet is what data being transported across the internet is split into.
A packet is made up of the header and the payload.
What is an NIC?
A Network Interface Card is hardwired with a unique MAC address and allows a computer to connect to a network.
What are the steps in packet switching?
- Data is split into packets.
- Header is added to packet
- Packets are sent along the network, not necessarily along the same route
- Once packets arrived, they are re-ordered using their sequence number
- Receipt message sent from recipient to sender
- Transmission happens again if no confirmation message is received
What is a protocol?
tbc
What does TCP/IP stand for?
Transmission Control Protocol / Internet Protocol
What are the four layers of the TCP/IP protocol and what does each layer do?
- Application Layer -
The application layer uses an appropriate protocol relating to whatever application is being used to transmit data - Transport Layer -
(uses TCP)
The transport layer is responsible for establishing the “end-to-end” connection and splitting the data into packets once the connection is made.
To each packet, the transport layer adds:- The sequence number
- The total number of packets
- The port number the packet should use
- Network Layer (aka internet layer)-
(uses IP)
Adds:- Source IP address
- Destination IP address
(used by routers)
- Link layer
The link layer is responsible for adding the MAC addresses of the source and destination device.
This MAC address is changed at each hop on the route
What is a MAC address?
The Media Access Control address is a unique 12-digit hexadecimal address hardcoded on each NIC for use as an address in network communications to uniquely identify any device.
What is a socket in the context of TCP/IP and routing packets?
A socket is the IP address (provided by the IP protocol) combined with the port (provided by the TCP protocol)
What is a port in the context of TCP/IP and routing packets?
The port determines what application on the device needs the packet
What does FTP stand for and what is its purpose?
File Transfer Protocol
Used to move files between two devices. (commonly used to transfer data and programs as opposed viewable content)
What does HTTP stand for and what is its purpose?
Hypertext Transfer Protocol
HTTP is used for accessing a webpage from a web server
What does HTTPS stand for and what is its purpose?
Hypertext Transfer Protocol Secure
HTTPS is used for accessing a webpage from a web server securely. HTTPS encrypts data between the client and server.
What does POP3 stand for and what is its purpose?
Post Office Protocol (v3)
Used to retrieve emails from an email server.
What does SMTP stand for and what is its purpose?
Simple Mail Transfer Protocol
Used to send emails from client device to the linked mail server or to forward the email to the recipient’s mail server.
What does SSH stand for and what is its purpose?
Secure Shell
Used to provide an encrypted connection for remove access to another computer.
How does FTP work?
FTP commands can be issued from a command line interface, but more commonly a user interacts with an FTP client, which sits on top of the actual FTP protocol.
Once logged in, the user can access directories on the FTP server and can download and upload files.
FTP sites which are publicly available are known as anonymous FTP.
How does HTTP work?
The web client sends a request message to a web server and the web server sends back a response message containing the data needed to display the webpage.
How does HTTPS work?
HTTPS uses encryption to secure the data being transferred, and authenticates the web server through certificates.
How does POP3 work?
POP3 retrieves emails from a mail server, removes it from the server and transfers in to your device.
How does SMTP work?
SMTP sends the email from the client device to the linked mail server or forwards the email to the recipient’s mail server.
How does SSH work?
SSH uses for port 22. It uses public key encryption to authenticate the user and prevent unauthorised access.
- The client initiates the connection by contacting the server.
- The server sends a public key to the client
- The server and client agree communication rules and open a secure channel.
- The user can now login to the remote server host OS and can issue commands
SSH can be used to tunnel through firewalls on port 22 to use other application level protocols.
