/lib/firewalld/services/ Current File: //lib/firewalld/services/mqtt.xml

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>mqtt</short>
  <description>The Message Queuing Telemetry Transport (MQTT) is a machine-to-machine connectivity protocol. This variant of the protocol is unencrypted.</description>
  <port port="1883" protocol="tcp"/>
</service>