IANA-registered to Common Trace Facility; effectively never seen in the wild.
Port 84 is registered with IANA as ctf, Common Trace Facility, an early tracing/diagnostics service registered by Hugh Thomas. No RFC defines it and no widely deployed implementation uses it, so the registration is the whole of the public record. It still appears in every system /etc/services file, which is why scanners label an open 84 as "ctf" regardless of what is actually listening. If you find 84 open, treat the name as meaningless and identify the service by its banner.
Expose with care
Nothing standard runs here, so an open 84 is an unidentified service — fingerprint it before deciding anything.
$ nc -vz TARGET 84Seen 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.