Reserved at IANA — the old compressnet registration was de-assigned in 2025.
Port 3 carried the 'compressnet' Compression Process registration for decades, alongside port 2 for its management utility. IANA de-assigned both on 2025-02-13 and now marks them Reserved, so no service owns this number. There is no protocol here to speak of and no software in common use that binds it. If a scan shows port 3 open, the service is unidentified and you have to fingerprint it directly.
Expose with care
Nothing is registered here, so an open port 3 is an unidentified listener — identify what owns the socket before deciding anything.
$ nc -vz TARGET 3Seen 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.