Step-by-Step Exercises

Trace through protocol and network processes

How to Use These Exercises

Work through each step carefully. Click "Show Next Step" to reveal each stage, and think about what happens before revealing the answer.

Exercise 1: Loading a Secure Web Page (HTTPS)

Scenario: A student types https://www.school.ac.uk into their browser. Trace the process from request to page display.

Step 1

DNS Lookup

Browser sends a DNS query to find the IP address for "www.school.ac.uk".

DNS returns: 185.230.63.107

Step 2

TCP Connection Established

Browser establishes a TCP connection to port 443 (HTTPS) on the server.

Three-way handshake completes - connection ready.

Step 3

TLS/SSL Handshake

Browser and server negotiate encryption. Server sends its certificate to prove identity.

🔒 Encrypted connection established. Padlock icon appears in browser.

Step 4

HTTP Request (Encrypted)

Browser sends encrypted HTTP GET request: "Please send me the homepage".

Request: GET / HTTP/1.1 Host: www.school.ac.uk

Step 5

Server Processes Request

Web server receives and decrypts the request. Finds the homepage HTML file.

Server prepares response with HTML content.

Step 6

Response Sent (Encrypted)

Server encrypts and sends the HTML back to the browser.

Response: HTTP/1.1 200 OK + encrypted HTML content

Step 7

Page Displayed

Browser decrypts response, parses HTML, and renders the page.

Student sees the school website with 🔒 indicating secure connection.

Exercise complete! You've traced an HTTPS web request.

Exercise 2: Sending an Email

Scenario: Alice (alice@gmail.com) sends an email to Bob (bob@outlook.com). Trace the journey of the email.

Step 1

Alice Composes Email

Alice writes her email and clicks Send in her email client.

Email ready: To: bob@outlook.com, Subject: "Hello Bob!"

Step 2

SMTP: Client to Gmail Server

Alice's email client uses SMTP to send the email to Gmail's mail server.

Email received by smtp.gmail.com

Step 3

DNS Lookup for Recipient

Gmail server looks up the mail server for outlook.com (MX record).

Found: outlook-com.olc.protection.outlook.com

Step 4

SMTP: Gmail to Outlook Server

Gmail's server uses SMTP to forward the email to Outlook's mail server.

Email delivered to Microsoft's mail server.

Step 5

Email Stored in Bob's Mailbox

Outlook server places the email in Bob's inbox, waiting to be retrieved.

Email stored on server. Bob has 1 new message.

Step 6

IMAP/POP3: Bob Retrieves Email

Bob's email client uses IMAP (or POP3) to download the email from the server.

Email appears in Bob's inbox - "Hello Bob!" from Alice.

Exercise complete! You've traced email protocols: SMTP (sending) and IMAP/POP3 (receiving).

Exercise 3: Data Through the TCP/IP Layers

Scenario: A user submits a form on a website. Trace the data as it moves down through the TCP/IP layers before transmission.

Step 1

Application Layer

User fills in form data. Browser creates an HTTP POST request with the form data.

Data: Form contents (name, email, message) + HTTP headers

Step 2

Transport Layer (TCP)

TCP breaks data into segments. Adds source port, destination port (80 or 443), and sequence numbers.

Data now has: Port 12345 → Port 443, sequence number, checksum

Step 3

Internet Layer (IP)

IP adds source and destination IP addresses. Creates packets for routing.

Data now has: From 192.168.1.50 → To 203.0.113.45

Step 4

Network Access Layer

MAC addresses added for local network delivery. Data converted to frames.

Data now has: MAC 00:1A:2B:3C:4D:5E → Router MAC

Step 5

Physical Transmission

Frames converted to electrical signals (Ethernet) or radio waves (WiFi) and transmitted.

Data physically travels through cable/air to the router.

Step 6

At Destination: Reverse Process

Server receives data and passes it up through layers, removing headers at each level.

Web server receives original form data and processes submission.

Exercise complete! You've traced data encapsulation through TCP/IP layers.

Exercise 4: Uploading a Website via FTP

Scenario: A web developer uploads a new index.html file to their web server using an FTP client.

Step 1

Connect to FTP Server

Developer opens FTP client and enters server address: ftp.mywebsite.com

Connection established to FTP server on port 21.

Step 2

Authentication

Developer enters username and password. Server verifies credentials.

Step 3

Navigate to Destination

FTP client shows remote directory structure. Developer navigates to /public_html/

Current directory: /public_html/ (contains old website files)

Step 4

Initiate Upload

Developer drags index.html from local computer to remote directory. FTP STOR command sent.

Upload starting: index.html (45 KB)

Step 5

Data Transfer

File data transferred over a separate data connection. Progress bar shows transfer.

Transferring: 45 KB at 150 KB/s... 100% complete.

Step 6

Upload Complete

Server confirms file received. New index.html replaces the old one on the web server.

File uploaded successfully. Website updated!

Exercise complete! You've traced an FTP file upload process.

Exercise 5: Connecting to a WiFi Network

Scenario: A student connects their laptop to the school WiFi network for the first time.

Step 1

WiFi Scan

Laptop's wireless NIC scans for available networks. Detects "School-WiFi" network.

Available networks: School-WiFi (secured), Guest-WiFi, CafeNext

Step 2

Network Selection

Student clicks on "School-WiFi". System prompts for password (WPA2 encryption).

Prompt: "Enter password for School-WiFi"

Step 3

Authentication

Student enters password. Laptop sends credentials to the Wireless Access Point (WAP).

WAP verifies password against stored credentials.

Step 4

Encryption Key Exchange

WAP and laptop negotiate encryption keys. All future traffic will be encrypted.

🔒 Encrypted connection established using WPA2.

Step 5

DHCP: IP Address Assignment

Laptop sends DHCP request. Server assigns an IP address from the school's range.

Assigned IP: 10.50.12.87, Gateway: 10.50.12.1, DNS: 10.50.1.1

Step 6

Connected!

Laptop is now fully connected to the network and can access the internet.

Status: "Connected to School-WiFi" - student can browse, email, etc.

Exercise complete! You understand WiFi connection with WPA2 encryption.

Exercise 6: How IP and MAC Addresses Work Together

Scenario: Computer A (IP: 192.168.1.10) needs to send data to Computer B (IP: 192.168.1.20) on the same local network. Trace how addresses are used.

Step 1

Application Creates Data

An application on Computer A wants to send data to Computer B (IP: 192.168.1.20).

Destination IP known: 192.168.1.20. But what's the MAC address?

Step 2

ARP Request

Computer A broadcasts an ARP (Address Resolution Protocol) request: "Who has 192.168.1.20?"

ARP broadcast sent to all devices on the network.

Step 3

ARP Reply

Computer B recognises its IP address and responds with its MAC address.

ARP reply: "192.168.1.20 is at MAC 00:2B:3C:4D:5E:6F"

Step 4

ARP Cache Updated

Computer A stores the IP-to-MAC mapping in its ARP cache for future use.

Cache: 192.168.1.20 → 00:2B:3C:4D:5E:6F (cached for efficiency)

Step 5

Frame Created

Computer A creates an Ethernet frame with both IP and MAC addresses.

Frame: Dest MAC 00:2B:3C:4D:5E:6F, Dest IP 192.168.1.20

Step 6

Switch Delivers Frame

The switch uses the destination MAC address to forward the frame only to Computer B's port.

Data successfully delivered to Computer B.

Exercise complete! You understand how IP and MAC addresses work together.

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