{
  "port": 3,
  "protocol": "tcp",
  "service": "Reserved (formerly compressnet)",
  "oneLiner": "Reserved at IANA — the old compressnet registration was de-assigned in 2025.",
  "whatItIs": "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.",
  "exposure": {
    "verdict": "careful",
    "note": "Nothing is registered here, so an open port 3 is an unidentified listener — identify what owns the socket before deciding anything."
  },
  "checkCommand": "nc -vz TARGET 3",
  "links": [
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml",
      "kind": "iana"
    }
  ]
}