Port 21: FTP
Port 21 is the FTP control channel, where the client sends commands like USER, PASS, and RETR. Plain FTP is unencrypted, so prefer SFTP (port 22) or FTPS.
| Port number | 21 |
|---|---|
| Service | File Transfer Protocol (control) |
| Protocol | TCP |
| Category | File transfer |
| Default encryption | No |
How do I check whether port 21 is open?
Port 21 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 21 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 21 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':21 ' | Lists the process bound to port 21 on Linux. On macOS use lsof -nP -iTCP:21 -sTCP:LISTEN, on Windows netstat -ano | findstr :21 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 21 used for?
Port 21 is the FTP control channel, where the client sends commands like USER, PASS, and RETR. Plain FTP is unencrypted, so prefer SFTP (port 22) or FTPS.
Is port 21 TCP or UDP?
Port 21 (FTP) uses TCP.
Is port 21 secure?
Port 21 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 21 on my firewall?
Only if you specifically need FTP. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.