Unregistered high port with no standard service — it shows up on scans slightly more often than its neighbours, and nobody has named what is behind it.
Like the rest of 49152-65535, 65389 is in the Dynamic/Private range that RFC 6335 keeps unassignable, so IANA has no entry for it. Nmap's database calls it unknown but records it open on roughly 0.076% of scanned hosts — around 269th by frequency, tied with nineteen other ports at that value, which is high for an unnamed port and suggests some product or convention puts a listener there without documenting it. No public source names the service behind it. Otherwise it behaves as any ephemeral port does: Windows and macOS/BSD pick outbound source ports from this range, so most sightings are client sockets rather than servers.
Expose with care
An unidentified listener on an unregistered port is the thing to investigate, not to expose. Find the process first; the verdict belongs to whatever protocol it turns out to speak.
$ sudo lsof -nP -iTCP:65389 -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.