Port 1883 (MQTT)

MQTT publish/subscribe protocol for IoT devices and home automation (Mosquitto, EMQX, Home Assistant).

Registered (user) port, 1024-49151 TCP IoT and devices Do not expose to the internet

What port 1883 is used for

MQTT publish/subscribe protocol for IoT devices and home automation (Mosquitto, EMQX, Home Assistant).

Security: should port 1883 be open?

Do not expose to the internet. Plain MQTT has no encryption, and many brokers allow anonymous access; open brokers leak sensor data and let anyone control devices. Use 8883 with TLS and require credentials.

IANA assignment

Service nameProtoDescriptionAssigneeReference

mqtt TCP Message Queuing Telemetry Transport Protocol OASIS -

mqtt UDP Message Queuing Telemetry Transport Protocol OASIS -

Registry dates for this port: last modified 2015-02-10.

Check what is listening on port 1883

Linux: is anything listening on TCP 1883?

sudo ss -tlnp 'sport = :1883'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1883

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1883 '

Windows (Command Prompt)

netstat -ano | findstr :1883

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1883 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 1883

From Windows

Test-NetConnection HOST -Port 1883

Block port 1883 in the firewall

ufw

sudo ufw deny 1883/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1883 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1883 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1883' -Direction Inbound -Protocol TCP -LocalPort 1883 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.