Registered to an ancient Stanford/MIT Telnet gateway; nothing runs it today.
IANA records port 89 as su-mit-tg, the SU/MIT Telnet Gateway, registered by Mark Crispin. It was a gateway service between Stanford and MIT networks in the early Internet and has no surviving specification or implementation. Modern scans that report "su-mit-tg" are just echoing /etc/services. In practice an open 89 is an unrelated service parked one port above 88.
Expose with care
No standard service claims this port in practice, so an open 89 needs fingerprinting before you trust it.
$ nc -vz TARGET 89Seen 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.