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FTP data connection failed

Why FTP data connections fail and how to troubleshoot passive and active data channel issues.

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.

FTP uses a separate data connection for directory listings and file transfers.

If the data connection fails, operations like LIST or file transfers may hang or fail.

Common causes

  • Firewall blocking passive ports
  • Incorrect PASV configuration
  • NAT address mismatch
  • Server passive port range not open

Fix checklist

  1. Configure a passive port range on the server.
  2. Open that port range in the firewall.
  3. Ensure the server advertises the correct public IP.
  4. Test with passive mode enabled.
FTPMonitor Help

Still stuck? We can help diagnose and fix it.

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