Telnet wrapped in TLS — registered, sporadically implemented, and still Telnet underneath.
IANA registers 992 as telnets: a Telnet session where TLS is negotiated the moment the connection opens, instead of in-band. No IETF standard defines it — the in-band route, Telnet START_TLS, never got past a draft — so support is vendor-specific and turns up mostly on IBM i systems, terminal servers, and network appliances. It is rare on scans, and much rarer than cleartext Telnet on 23. Encrypted transport or not, what waits at the far end is a login prompt on a device that predates SSH support.
Expose with care
The session is encrypted, which is the whole point, but this is still interactive administrative access over a legacy protocol with no standard behind this port. Use SSH where the device supports it and keep 992 on a management network otherwise.
$ openssl s_client -connect TARGET:992 -quietSeen 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.