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FTP passive mode not working

Why FTP passive mode fails and how to configure passive ports and NAT correctly.

Diagnose this automatically

Test whether the server allows directory listing with valid credentials.

terminal
npx ftpmonitor check --protocol ftp --host ftp.example.com --port 21 --username user --password pass --path /incoming
Shareable output
terminal
npx ftpmonitor check --protocol ftp --host ftp.example.com --port 21 --username user --password pass --path /incoming --format slack --copy

Prefer the browser? Run the same check on the homepage.

Passive mode allows the FTP server to open a data port for transfers.

If passive mode fails, directory listings or file transfers will not work.

Common causes

  • Passive port range not configured
  • Firewall blocking passive ports
  • Incorrect external IP advertised
  • NAT configuration errors

Fix checklist

  1. Configure a fixed passive port range.
  2. Open passive ports in the firewall.
  3. Set correct external IP in server configuration.
  4. Test passive mode from outside the network.
Related
Diagnostics powered by FTPMonitor CLI