Topic 9.4.2 - Application Layer Protocols

Question 1

Explain the FTP (File Transfer Protocol)

Answer 1

Used for sending files between devices.

FTP services can be accessed anonymously or non-anonymously by using a username and password

Question 2

Explain HTTP (Hypertext Transfer Protocol)

Answer 2

Delivers websites held by the web servers.

Question 3

Explain HTTPS (Hypertext Transfer Protocol Secure)

Answer 3

Delivers websites held by the web server however it encrypts the information during this transmission

Question 4

Explain POP3 (Post Office Protocol V3)

Answer 4

Used for retrieving emails from an email server.
Communicates with the server to check for any new messages

Question 5

Explain SMTP (Simple Mail Transfer Protocol)

Answer 5

Used for sending emails.
Used between the client and the email server

Question 6

Explain SSH (Secure Shell)

Answer 6

Used to remotely manage computers.
Requires a username / password in order to be able to remotely manage.
Encyrpts information during transmission.

Question 7

How is Secure Shell used for remote management

Answer 7

Provides encrypted connections between the client and a remote device allowing them to communicate with each other.

Question 8

How and why does a SSH client make a TCP connection to a remote port.

Answer 8

While other ports on a server may be blocked by the firewall, the SSH port will not be blocked, so it can make a TCP connection to the remote port.

Then you can send other requests like SMTP and POP3 even though they are blocked for everyone else who doesnt have access to the SSH

Question 9

How is SSH secure

Answer 9

A username & password combination is needed to allow access to a remote computer

Information is encrypted during transmission

Question 10

Explain the role of an email server in sending and retrieving emails

Answer 10

Email server works alongside POP3 and SMTP and are responsible for receiving and sending emails

SMTP sends email to email server.

Email server retrieves this email and communicates with POP3 to tell them there is an email ready to be collected

POP3 downloads the new email

Question 11

Explain the role of a web server in displaying web pages in text form

Answer 11

Get request sent from browser to web server

Web server sends file to browser.

If there are multiple resources (text, video, photo) there will need to be a separate GET request for each additional resource

Browser displays webpage according to the HTML code

Question 12

Explain the role of a web browser in retrieving web pages and resources.

Answer 12

Web browser receives Domain name from user.

Browser sends FQDN to DNS which returns the IP address.

Browser sends a GET request using the IP address to the Web server.

Web server sends the webpage to Browser

If multiple resources (image,video,links), a separate GET request will need to be performed for each resource

Browser displays webpage according to the HTML and CSS code.