Port 1883: MQTT
Port 1883 is MQTT, a lightweight publish-subscribe messaging protocol built for IoT devices with limited bandwidth or power. A device publishes to a topic and a broker fans the message out to every subscriber, without sender and receiver needing to connect directly.
| Port number | 1883 |
|---|---|
| Service | MQTT publish-subscribe messaging |
| Protocol | TCP |
| Category | IoT & automation |
| Default encryption | No |
How do I check whether port 1883 is open?
Port 1883 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 1883 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 1883 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':1883 ' | Lists the process bound to port 1883 on Linux. On macOS use lsof -nP -iTCP:1883 -sTCP:LISTEN, on Windows netstat -ano | findstr :1883 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 1883 used for?
Port 1883 is MQTT, a lightweight publish-subscribe messaging protocol built for IoT devices with limited bandwidth or power. A device publishes to a topic and a broker fans the message out to every subscriber, without sender and receiver needing to connect directly.
Is port 1883 TCP or UDP?
Port 1883 (MQTT) uses TCP.
Is port 1883 secure?
Port 1883 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 1883 on my firewall?
Only if you specifically need MQTT. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.