Tools / Port checker / 21
Is port 21 open?
Port 21 is FTP. Enter your server below to test it from Dallas, Amsterdam and London.
What port 21 is used for
File Transfer Protocol control channel. Clients connect here to log in and send commands; data moves over separate ports.
Should port 21 be open?
Open it only to the addresses that need it. FTP sends passwords in plain text. Use SFTP over SSH (port 22) instead, or FTPS if a client requires FTP.
How to open port 21
Ubuntu or Debian with ufw, allowing only your own address (replace 203.0.113.10):
sudo ufw allow from 203.0.113.10 to any port 21 proto tcp
Rocky, Alma or CentOS with firewalld:
sudo firewall-cmd --permanent --add-port=21/tcp && sudo firewall-cmd --reload
Windows Server, in PowerShell as administrator:
New-NetFirewallRule -DisplayName "Port 21" -Direction Inbound -Protocol TCP -LocalPort 21 -Action Allow
Then check that the service listens on all addresses, not only 127.0.0.1, and test again above.
Check another port
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Run your service on a PrivateByte server: a firewall you control and every port yours to open.