{
  "port": 3390,
  "protocol": "both",
  "service": "dsc (Distributed Service Coordinator)",
  "oneLiner": "Registered as Distributed Service Coordinator, but in practice the port next door to RDP.",
  "whatItIs": "IANA assigns 3390 to dsc, \"Distributed Service Coordinator\", registered to Charles Honton with no published specification. Nothing in common use implements it. What you actually find on 3390 is usually a second RDP listener: when two Windows hosts sit behind one NAT, or an admin wants RDP off the obvious port, 3390 is the reflexive next choice. That is convention, not registration — confirm by fingerprinting rather than assuming.",
  "exposure": {
    "verdict": "careful",
    "note": "If a fingerprint shows RDP here, apply the 3389 rule and keep it off the internet; if it is something else, identify the process before deciding."
  },
  "checkCommand": "nmap -Pn -sV -p 3390 TARGET",
  "links": [
    {
      "title": "IANA port registry — 3390 (dsc)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=3390",
      "kind": "iana"
    }
  ]
}