In this chapter, we worked with different tools to interact with the Mosquitto MQTT 3.1.1 server we installed in Chapter 1, Installing an MQTT 3.1.1 Mosquitto Server. We worked with an unsecured MQTT server to easily understand the interaction between the MQTT clients and the MQTT server.

We subscribed to topics via the command-line and GUI tools. Then, we published messages with QoS level 0 and we unsubscribed from topics. We learned best practices related to topics; and single-level, and multilevel wildcards. We studied in detail the different Quality of Service levels supported by MQTT and when it is appropriate to use each of them. We analyzed their advantages and disadvantages.

Now that we understood how the MQTT 3.1.1 basics work, we will learn how to secure an MQTT server and to follow best practices related to security, which are the topics that we are going to discuss in Chapter 3, Securing an MQTT 3.1.1 Mosquitto Server.