Step-by-Step Exercises

Trace through network processes and understand how data travels

How to Use These Exercises

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

Exercise 1: DNS Lookup Process

Scenario: A user types "www.bbc.co.uk" into their web browser. Trace the DNS lookup process.

Step 1

Browser checks local cache

The browser first checks if it has recently visited this website and has the IP address stored in its local cache.

Cache miss - the IP address is not stored locally.

Step 2

Query sent to DNS resolver

The computer sends a DNS query to the configured DNS resolver (usually provided by the ISP or set manually like 8.8.8.8).

Query: "What is the IP address for www.bbc.co.uk?"

Step 3

DNS resolver queries root server

If the resolver doesn't have the answer cached, it asks a root DNS server which directs it to the .uk TLD servers.

Root server responds: "Ask the .uk name servers"

Step 4

Query to authoritative DNS server

The resolver eventually reaches the BBC's authoritative DNS server which has the actual IP address mapping.

Response: "www.bbc.co.uk = 151.101.0.81"

Step 5

IP address returned to browser

The DNS resolver caches the result and returns the IP address to the user's computer. The browser can now connect directly to 151.101.0.81.

Browser now connects to the web server using the IP address.

Exercise complete! You've traced a DNS lookup process.

Exercise 2: Client-Server Web Request

Scenario: A student searches for "computer networks" on a school library website. Trace the client-server interaction.

Step 1

Client sends request

The student's computer (client) sends an HTTP request to the library web server. The request includes the search query "computer networks".

HTTP GET request sent with search parameters.

Step 2

Server receives and processes request

The web server receives the request and queries its database for books matching "computer networks".

Server finds 15 matching book records.

Step 3

Server generates response

The server creates an HTML page containing the search results, including book titles, authors, and availability status.

HTML response page generated with 15 results.

Step 4

Server sends response to client

The server sends the HTTP response containing the HTML page back to the student's computer through the network.

HTTP 200 OK response with HTML content.

Step 5

Client displays results

The browser on the student's computer receives the HTML, renders it, and displays the search results on screen.

Student sees the list of 15 books about computer networks.

Exercise complete! You've traced a client-server web request.

Exercise 3: Packet Journey Through a Network

Scenario: An email is sent from a computer in the Marketing department to the Finance department in a large office LAN. Trace the packet's journey.

Step 1

Data prepared by sender's NIC

The marketing computer's Network Interface Card (NIC) prepares the email data, adding the destination MAC and IP addresses.

Packet created with header information and email payload.

Step 2

Packet reaches the switch

The packet travels through the Ethernet cable to the Marketing department's network switch.

Switch receives the packet on port 3.

Step 3

Switch consults MAC address table

The switch reads the destination MAC address and looks up which port to forward the packet to. It determines the packet needs to go to the router.

MAC address found - forward to port 24 (router).

Step 4

Router determines destination network

The router reads the destination IP address and determines the Finance department is on a different subnet. It consults its routing table.

Route to Finance subnet found - forward to Finance switch.

Step 5

Finance switch delivers packet

The Finance department's switch receives the packet and uses its MAC address table to forward it to the correct computer.

Packet delivered to the destination computer's NIC.

Step 6

Recipient's NIC processes packet

The Finance computer's NIC receives the packet, strips the headers, and passes the email data to the email application.

Email appears in the recipient's inbox.

Exercise complete! You've traced a packet's journey through a LAN.

Exercise 4: Star Topology Failure Scenario

Scenario: In a school computer lab with a star topology, the central switch suddenly fails. Trace what happens to network communication.

Step 1

Initial state: Normal operation

30 computers are connected to a central switch. Students are printing, accessing the internet, and sharing files.

All network traffic flows through the central switch.

Step 2

Switch failure occurs

A power surge causes the central switch to fail. It stops processing all network traffic immediately.

All ports on the switch go down simultaneously.

Step 3

Immediate network isolation

All 30 computers lose connectivity. No computer can communicate with any other computer or network resource.

Network connection icons show "disconnected" on all computers.

Step 4

Services become unavailable

Students cannot: access the internet, print documents, save to network drives, or access shared resources.

Error messages appear: "Network path not found", "Printer offline".

Step 5

Single point of failure demonstrated

This illustrates the main disadvantage of star topology - the entire network depends on the central switch. One failure affects everyone.

Total network outage until switch is replaced or repaired.

Exercise complete! You understand star topology's single point of failure.

Exercise 5: Mesh Network Resilience

Scenario: A hospital uses a mesh network for critical systems. One network cable is accidentally cut during construction work. Trace how the network responds.

Step 1

Initial state: Normal operation

The mesh network connects 6 critical systems (A, B, C, D, E, F). Each device has multiple direct connections to other devices.

Device A connects to B, C, and D. Device B connects to A, C, E, etc.

Step 2

Cable cut between A and B

Construction work accidentally severs the cable connecting Device A directly to Device B.

Direct A-B connection lost. Network detects the failure.

Step 3

Automatic route recalculation

The network routing protocol detects the failed link and recalculates paths. Device A can still reach B via alternative routes.

New route found: A → C → B (via device C).

Step 4

Traffic rerouted automatically

All traffic that previously used the A-B link is now routed through alternative paths. This happens automatically with minimal delay.

Communication continues - slight increase in latency on affected routes.

Step 5

Network remains fully operational

Unlike star topology, the mesh network continues operating despite the failure. Critical hospital systems remain connected.

No service disruption - mesh topology's redundancy has protected the network.

Exercise complete! You understand mesh topology's fault tolerance.

Exercise 6: Accessing Files from the Cloud

Scenario: A student opens a document stored in Google Drive from their home computer. Trace the process.

Step 1

User initiates request

The student logs into Google Drive in their web browser and clicks on a document called "History Essay.docx".

Browser sends request to drive.google.com with authentication credentials.

Step 2

Request travels to Google's data centre

The request travels across the internet through multiple routers, potentially crossing countries, to reach Google's cloud servers.

Request arrives at a Google data centre (possibly in Ireland or Belgium for UK users).

Step 3

Server authenticates and locates file

Google's servers verify the student's login credentials, check file permissions, and locate the document across their distributed storage system.

File found and access confirmed - student owns the document.

Step 4

File data transmitted

The document data is sent from Google's servers back across the internet to the student's computer.

Document data (250KB) transmitted via encrypted HTTPS connection.

Step 5

Document opens in browser

Google Docs renders the document in the browser. The student can now read and edit the file - changes will sync back to the cloud.

Student sees their History Essay and can continue working on it.

Exercise complete! You understand how cloud storage works.

Exercise 7: Diagnosing Slow Network Performance

Scenario: Students in an ICT lesson complain that the internet is very slow. The technician investigates. Trace the diagnostic process.

Step 1

Check number of connected devices

The technician logs into the network switch and counts active connections. They find 32 devices connected to a network designed for 25.

Finding: Network is overloaded with too many devices.

Step 2

Check bandwidth usage

Network monitoring shows that 3 computers are streaming 4K video (using 75% of available bandwidth).

Finding: High bandwidth activities are consuming most capacity.

Step 3

Test network latency

The technician runs a ping test to the router. Latency is 150ms when it should be under 5ms.

Finding: High latency indicates congestion or hardware issues.

Step 4

Check transmission media

Physical inspection reveals a damaged Ethernet cable to the main switch - it's kinked and partially severed.

Finding: Physical cable damage is causing packet loss and retransmissions.

Step 5

Identify root causes

Multiple factors are causing slow performance: (1) too many devices, (2) bandwidth-heavy activities, and (3) damaged cabling.

All three network performance factors are contributing to the problem.

Step 6

Apply solutions

The technician: (1) replaces the damaged cable, (2) asks teacher to stop video streaming, (3) recommends capacity planning for future.

Network speed returns to normal after fixing the physical cable.

Exercise complete! You've traced a network troubleshooting process.

Exercise 8: Peer-to-Peer File Sharing

Scenario: In a home network, one family member wants to share a large video file with another family member. Trace the peer-to-peer transfer.

Step 1

File sharing enabled

Computer A enables file sharing and makes the video file available on the network. No central server is involved.

File "holiday_video.mp4" (2GB) is shared on the local network.

Step 2

Computer B discovers shared file

Computer B browses the network and finds Computer A. It can see the shared video file.

Network discovery shows Computer A with 1 shared file.

Step 3

Direct connection established

Computer B connects directly to Computer A - no intermediary server is needed. Both computers act as equals (peers).

Direct peer-to-peer connection established over home WiFi.

Step 4

File transfer begins

The video file is transferred directly from Computer A to Computer B. Computer A sends the data, Computer B receives it.

Transfer speed: 50MB/s - estimated time 40 seconds.

Step 5

Transfer completes

The file is now on both computers. Either computer could now share the file with others - demonstrating the equal nature of P2P networks.

Both computers now have a copy of the video file.

Exercise complete! You understand peer-to-peer file sharing.

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