MQTT broker role in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start an MQTT broker using the popular Mosquitto service.

IOT Protocols

sudo systemctl [1] mosquitto

Drag options to blanks, or click blank then click option'

Astop

Bstatus

Cstart

Drestart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' instead of 'start' stops the service.

Using 'status' only shows the service status but does not start it.

The start command launches the Mosquitto MQTT broker service.

2fill in blank

medium

Complete the command to check if the MQTT broker is running.

IOT Protocols

sudo systemctl [1] mosquitto

Drag options to blanks, or click blank then click option'

Adisable

Benable

Cstart

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' will try to launch the service instead of checking it.

Using 'enable' or 'disable' changes startup behavior but does not show running status.

The status command shows if the Mosquitto broker is active and running.

3fill in blank

hard

Fix the error in the command to restart the MQTT broker.

IOT Protocols

sudo systemctl [1] mosquitto

Drag options to blanks, or click blank then click option'

Astop

Brestart

Creload

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reload' may not fully restart the service.

Using 'stop' only stops the service without starting it again.

The restart command stops and then starts the Mosquitto broker, applying any changes.

4fill in blank

hard

Fill both blanks to create a command that enables the MQTT broker to start automatically on boot and then start it now.

IOT Protocols

sudo systemctl [1] mosquitto && sudo systemctl [2] mosquitto

Drag options to blanks, or click blank then click option'

Aenable

Bstart

Cstop

Ddisable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' or 'disable' will prevent the broker from running.

Reversing the order may start the service but not enable it on boot.

enable sets the broker to start on boot, and start runs it immediately.

5fill in blank

hard

Fill all three blanks to create a command that shows the MQTT broker logs, filters for errors, and limits output to the last 10 lines.

IOT Protocols

sudo journalctl -u mosquitto | grep [1] | tail -n [2]

Drag options to blanks, or click blank then click option'

Awarning

Berror

C10

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'warning' or 'info' filters different log levels.

Not limiting lines may show too much output.

This command filters Mosquitto logs for error messages and shows the last 10 lines.

Practice

1. What is the main role of an MQTT broker in IoT communication?

easy

A. To receive messages from devices and forward them to subscribers

B. To generate sensor data for devices

C. To act as a device that publishes messages only

D. To encrypt messages between devices

Solution

1. Step 1: Understand MQTT broker function

   The MQTT broker acts as a middleman that receives messages from publishers and forwards them to subscribers.

2. Step 2: Eliminate incorrect roles

   Generating data, acting only as a publisher, or encrypting messages are not the broker's main roles.

3. Final Answer:

   To receive messages from devices and forward them to subscribers -> Option A

4. Quick Check:

   Broker = message receiver and forwarder [OK]

Hint: Broker forwards messages between devices [OK]

Common Mistakes:

• Thinking broker generates data
• Confusing broker with publisher device
• Assuming broker only encrypts messages

2. Which network port does an MQTT broker usually listen on by default?

easy

A. 8080

B. 22

C. 443

D. 1883

Solution

1. Step 1: Recall default MQTT port

   The MQTT protocol commonly uses port 1883 for unencrypted communication.

2. Step 2: Identify other ports

   Port 8080 is for HTTP alternate, 443 for HTTPS, and 22 for SSH, not MQTT.

3. Final Answer:

   1883 -> Option D

4. Quick Check:

   MQTT default port = 1883 [OK]

Hint: MQTT default port is 1883 [OK]

Common Mistakes:

• Choosing common web ports like 80 or 443
• Confusing MQTT port with SSH port 22
• Assuming MQTT uses random ports

3. Given this MQTT broker behavior: A device publishes a message to topic home/livingroom/temperature. What does the broker do next?

medium

A. Sends the message to all devices regardless of subscription

B. Sends the message to all devices subscribed to home/livingroom/temperature

C. Deletes the message immediately after receiving

D. Saves the message locally and does not forward it

Solution

1. Step 1: Understand topic-based forwarding

   The MQTT broker forwards messages only to devices subscribed to the specific topic.

2. Step 2: Eliminate incorrect behaviors

   Broker does not just save or delete messages without forwarding, nor does it broadcast to all devices.

3. Final Answer:

   Sends the message to all devices subscribed to home/livingroom/temperature -> Option B

4. Quick Check:

   Broker forwards by topic subscription [OK]

Hint: Broker forwards messages only to subscribed topics [OK]

Common Mistakes:

• Assuming broker broadcasts to all devices
• Thinking broker stores messages without forwarding
• Believing broker deletes messages immediately

4. You configured an MQTT broker but devices cannot connect. Which of these is a likely cause?

medium

A. Broker is not listening on the correct port

B. Devices are publishing to the correct topic

C. Broker is forwarding messages correctly

D. Devices have correct subscription filters

Solution

1. Step 1: Check broker listening port

   If the broker is not listening on the expected port (usually 1883), devices cannot connect.

2. Step 2: Understand other options

   Publishing topics, forwarding messages, and subscription filters affect message flow but not initial connection.

3. Final Answer:

   Broker is not listening on the correct port -> Option A

4. Quick Check:

   Connection issue = wrong broker port [OK]

Hint: Check broker port if devices can't connect [OK]

Common Mistakes:

• Blaming topic or subscription before connection
• Ignoring broker network settings
• Assuming forwarding affects connection

5. You want to ensure that an MQTT broker only forwards messages to devices subscribed to topics starting with office/. Which broker feature helps achieve this?

hard

A. Device authentication

B. Message encryption

C. Topic filtering with wildcards

D. Retained messages

Solution

1. Step 1: Understand topic filtering

   MQTT brokers use topic filters with wildcards to forward messages only to matching subscriptions.

2. Step 2: Exclude unrelated features

   Encryption secures data, authentication controls access, and retained messages store last message; none filter topics.

3. Final Answer:

   Topic filtering with wildcards -> Option C

4. Quick Check:

   Topic filtering controls message forwarding [OK]

Hint: Use topic filters with wildcards to control forwarding [OK]

Common Mistakes:

• Confusing encryption with filtering
• Thinking authentication filters topics
• Assuming retained messages control forwarding