n ports

Port inspection (local listening or remote target ports)

Usage — n ports

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  Netscrew ("n") — ports (p, po, port) — Port inspection — local listeners, or an audit of a remote host
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USAGE:
  n p .                                list ports LISTENING on this machine
  n p . <tcp|udp|port|range>           filter local (e.g. . tcp, . 8080, . 8000 9000)
  n p <host>                           audit ~40 common ports on a remote host
  n p <host> <spec>                    specific ports: 22 · 22,443 · 8000-9000

OPTIONS:
  --full                           allow a wide audit (>2048 ports, e.g. <host> all)

Target: . = this machine · <host> = remote
Deeper: n p -h = the concept/theory behind this command

The concept behind it — n ports -h

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  NETSCREW PLAYBOOK: Port states ["port-states"]
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THREE ANSWERS:
  open      handshake completed → a service listens and the firewall lets you in
  closed    host answered "reset" → up and reachable, nothing there, no firewall in the way
  filtered  nothing came back → a firewall dropped it (host, router, or in between)
  "closed" PROVES reachability. "filtered" everywhere = a drop-by-default host firewall.

THE PORTS CHECKED FIRST:
  22 SSH · 3389 RDP · 5900 VNC    remote access — LAN-open normal, internet-open a risk
  445 SMB                         file sharing — never to the internet
  80/443 · 8080/8443 · 5000/9090  web UIs (n web <host> names them)     53 DNS     135/139 Windows RPC

Scope: your own machines. Wide audits (--full) are opt-in.