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MQTT (Message Queuing Telemetry Transport) is a lightweight publish-subscribe (pub/sub) protocol designed for efficient communication between systems, particularly in IoT, real-time data, and low-bandwidth environments.
MQTT Workflow
1. 🔐 Connect & Authenticate
- Publisher connects to the MQTT broker (Port `1883` for unencrypted, `8883` for TLS).
- Authentication via username/password or certificates.
2. 📤 Publish Message
- Publisher sends a message with a QoS level (0, 1, or 2) and an optional Retain flag.
3. 🧭 Route via Topic Tree
- Broker routes messages using topics (e.g.,
sensor/+/temperature).
4. 📬 Deliver to Subscribers
- Subscribers receive messages based on topic matching and QoS.
5. 📥 Subscribe to Topics
- Subscribers subscribe to topics to receive relevant messages.
You Should Know: MQTT Practical Implementation
1. Installing MQTT Broker (Mosquitto)
On Ubuntu/Debian sudo apt update sudo apt install mosquitto mosquitto-clients Start & Enable Mosquitto sudo systemctl start mosquitto sudo systemctl enable mosquitto Check status sudo systemctl status mosquitto
2. Basic MQTT Commands
Publish a Message:
mosquitto_pub -h localhost -t "test/topic" -m "Hello MQTT" -p 1883
Subscribe to a Topic:
mosquitto_sub -h localhost -t "test/topic" -p 1883
3. Python MQTT Example (Using Paho-MQTT)
import paho.mqtt.client as mqtt
def on_connect(client, userdata, flags, rc):
print("Connected with result code " + str(rc))
client.subscribe("test/topic")
def on_message(client, userdata, msg):
print(f"Received: {msg.topic} {msg.payload.decode()}")
client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.connect("localhost", 1883, 60)
client.loop_forever()
4. Securing MQTT with TLS
Generate Certificates openssl req -new -x509 -days 365 -nodes -out mosquitto.crt -keyout mosquitto.key Configure Mosquitto for TLS echo "listener 8883 cafile /etc/mosquitto/certs/mosquitto.crt keyfile /etc/mosquitto/certs/mosquitto.key certfile /etc/mosquitto/certs/mosquitto.crt" | sudo tee -a /etc/mosquitto/conf.d/ssl.conf Restart Mosquitto sudo systemctl restart mosquitto
5. MQTT QoS Levels
- QoS 0: At most once (Fire and forget)
- QoS 1: At least once (Guaranteed delivery)
- QoS 2: Exactly once (No duplicates)
What Undercode Say
MQTT is a powerful protocol for IoT, DevOps, and real-time messaging. Mastering it involves:
– Understanding topic hierarchy for efficient routing.
– Securing brokers with TLS & authentication.
– Using QoS levels appropriately for reliability.
– Integrating with Python, Node.js, or Go for automation.
Additional Useful Commands
Check active MQTT connections sudo netstat -tulnp | grep mosquitto Enable MQTT logging sudo tail -f /var/log/mosquitto/mosquitto.log Test MQTT with Docker docker run -it --rm -p 1883:1883 eclipse-mosquitto
Expected Output:
Connected with result code 0 Received: test/topic Hello MQTT
🔗 Further Reading:
References:
Reported By: Sandip Das – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
