{
  "port": 2001,
  "protocol": "tcp",
  "service": "dc (IANA) / Cisco reverse-telnet line 1",
  "oneLiner": "Registered as dc, but in practice the first reverse-telnet line on a Cisco terminal server.",
  "whatItIs": "IANA registers 2001/tcp as dc with no description. What you actually meet on this port is Cisco reverse telnet: on a terminal or comm server the listening port for an async line is 2000 plus the line number, so 2001 is line 1, and connecting drops you onto that line's attached console. Lab racks, out-of-band console servers, and console-server software that imitates the Cisco convention all use this numbering.",
  "exposure": {
    "verdict": "never",
    "note": "A reverse-telnet port is an unencrypted console session on someone else's device, frequently already logged in — this is out-of-band management and belongs on a management network reached over SSH or VPN."
  },
  "checkCommand": "nc -vz TARGET 2001",
  "links": [
    {
      "title": "Cisco — Configuring a Terminal/Comm Server (reverse telnet port = 2000 + line)",
      "url": "https://www.cisco.com/c/en/us/support/docs/dial-access/asynchronous-connections/5466-comm-server.html",
      "kind": "official-docs"
    },
    {
      "title": "IANA port registry — 2001 (dc)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=2001",
      "kind": "iana"
    }
  ]
}