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How to check if FTP port 21 is blocked
Find out how to test whether FTP port 21 is blocked on your network using the command line on Windows or Mac.
If you cannot connect to your FTP server, your ISP or company firewall may be blocking port 21. You can test this quickly from the command line.
Telnet is used here purely as a connectivity test. On Windows, you may need to enable the Telnet client before running the command (see below).
Windows
- Press Windows key + R to open the Run dialog, type
cmd, and press Enter. - In the Command Prompt window, run:
telnet yourdomain.com 21
Replace yourdomain.com with your actual domain name.
If you see the error "telnet is not recognised", you need to enable the Telnet client first. Go to Control Panel > Programs > Turn Windows features on or off, tick Telnet Client, and click OK.
Mac
- Open Finder, go to Applications > Utilities, and open Terminal.
- Run:
telnet yourdomain.com 21
Replace yourdomain.com with your actual domain name.
On macOS High Sierra and later, Telnet is not installed by default. You can install it via Homebrew (brew install telnet), or use nc -zv yourdomain.com 21 as an alternative.
Interpreting the results
If port 21 is open and reachable, you will see a response similar to:
220---------- Welcome to Pure-FTPd [TLS] ----------
220-You are user number 5 of 50 allowed.
220-Local time is now 03:35. Server port: 21.
220-This is a private system - No anonymous login
220-IPv6 connections are also welcome on this server.
220 You will be disconnected after 15 minutes of inactivity.
If you see anything else - such as a timeout, connection refused, or no output at all - port 21 is likely being blocked.
- If you are on a home connection, contact your ISP and ask them to unblock port 21.
- If you are on a work or office network, speak to your network administrator.
- As an alternative, ask your FTP client to connect using passive mode on port 21.
If you are still having trouble, contact Kualo support and we will be happy to help.