{
  "port": 5001,
  "protocol": "tcp",
  "service": "commplex-link / Synology DSM HTTPS / iperf 2",
  "oneLiner": "Registered as commplex-link, but in practice Synology DSM over HTTPS or an iperf 2 server.",
  "whatItIs": "The IANA name for 5001 is commplex-link, a registration with no public protocol behind it, so what you actually meet on this port is a squatter. On a home or small-office network it is usually a Synology NAS: DSM's web interface answers HTTP on 5000 and HTTPS on 5001 by default. On a lab or transit-test host it is more often an iperf 2 server, whose default listen port is 5001 (iperf3 moved to 5201).",
  "exposure": {
    "verdict": "careful",
    "note": "A DSM login page on the public internet is a brute-force magnet — put it behind a VPN or reverse proxy with MFA. An iperf server accepts traffic from anyone who finds it and should never be left running on a public address."
  },
  "checkCommand": "curl -sk -o /dev/null -w '%{http_code}\\n' https://TARGET:5001/",
  "links": [
    {
      "title": "Synology Knowledge Center — network ports used by Synology services",
      "url": "https://kb.synology.com/en-us/DSM/tutorial/What_network_ports_are_used_by_Synology_services",
      "kind": "official-docs"
    },
    {
      "title": "iPerf documentation — server port defaults (5001 for iPerf 2)",
      "url": "https://iperf.fr/iperf-doc.php",
      "kind": "official-docs"
    },
    {
      "title": "IANA port registry — 5001 (commplex-link)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=5001",
      "kind": "iana"
    }
  ]
}