Registered in 2009 to a commercial video-surveillance service and rarely seen anywhere else.
IANA registered 5566/tcp in 2009 as westec-connect, for Westec Intelligent Surveillance's managed video product; UDP 5566 is reserved rather than assigned. No protocol description was published, and no common software defaults to this port. Open on a host that is not part of a Westec installation, it is simply an application someone assigned there.
Expose with care
If it really is surveillance connectivity, video and camera control are sensitive traffic — confirm what is listening before letting it out.
$ nc -vz -w 3 TARGET 5566Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.