Internet-Security.com UDP port 5683 details

UDP port 5683 is the default port for the Constrained Application Protocol (CoAP).
OMA Lightweight M2M (LwM2M) device management runs over CoAP on this port; real deployments include servers like Eclipse Leshan and clients such as Eclipse Wakaama and AVSystem Anjay (used on devices like Nordic nRF9160-based products).
Shelly smart-home devices use CoAP on 5683 for local LAN discovery/status, which platforms like Home Assistant consume.
The IKEA TRÅDFRI gateway uses CoAP (commonly secure CoAPS on 5684), with 5683 used for unsecured CoAP in some setups/tools.
Common CoAP software stacks listen here by default, including libcoap’s coap-server, Eclipse Californium (cf-server), Node-CoAP, and CoAPthon.
OpenThread/Thread samples (e.g., OpenThread coap-server and Zephyr CoAP examples) use UDP 5683 for application-layer messaging within the mesh and for testing.
LwM2M/CoAP cloud services such as AVSystem Coiote Device Management and public Leshan demo servers expose 5683 for device registration, telemetry, and management.
Associated risk: openly exposed CoAP services on 5683 have been abused for UDP reflection/amplification DDoS attacks.

UDP 5683