Port 1883 is used for plain-text mqtt and 8883 is used for TLS+mqtt.
See: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=mqtt

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-- 
Hugo
diff --git etc/services etc/services
index 0405aa38d42..7f8c6143e9c 100644
--- etc/services
+++ etc/services
@@ -190,6 +190,8 @@ pptp		1723/tcp			# Point-to-Point Tunneling Protocol
 pptp		1723/udp			# Point-to-Point Tunneling Protocol
 radius		1812/udp			# radius authentication
 radacct		1813/udp	radius-acct	# radius accounting
+mqtt		1883/tcp			# Message Queuing Telemetry Transport Protocol
+mqtt		1883/udp			# Message Queuing Telemetry Transport Protocol
 ssdp		1900/tcp			# SSDP
 ssdp		1900/udp			# SSDP
 nfsd		2049/udp	nfs		# NFS server
@@ -275,6 +277,8 @@ afs3-rmtsys	7009/tcp			# AFS remote cache manager service
 afs3-rmtsys	7009/udp			# AFS remote cache manager service
 puppet		8140/tcp			# Puppet master service
 matrix-fed	8448/tcp			# Matrix Federation Protocol
+secure-mqtt	8883/tcp			# Secure MQTT
+secure-mqtt	8883/udp			# Secure MQTT
 ub-dns-control	8953/tcp			# unbound dns nameserver control
 git		9418/tcp			# git pack transfer service
 git		9418/udp			# git pack transfer service

• mqtt.diff (1004B)