Registered in 2014 to Zoom Control Panel, a game-server hosting panel — nothing to do with Zoom video conferencing.
IANA assigned 9666/tcp the service name zoomcp, "Zoom Control Panel Game Server Management"; the UDP side is marked Reserved. It belongs to a game-server hosting control panel that lets customers start, stop, and configure dedicated game servers. The name collision with the video-conferencing product is coincidental and a frequent source of confusion in port lookups. The registration is the substantial fact here — public protocol documentation is not available.
Do not expose
A hosting control panel is an administrative interface that starts and stops processes. If it must be reachable, put it behind a VPN or an authenticating reverse proxy with TLS.
$ sudo lsof -nP -iTCP:9666 -sTCP:LISTENSeen 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.
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Corrections or a missing port? Reply @rimrocksystems.