Port 21

ftp · SCTP/TCP/UDP

RangeSystem/well-known port (0–1023)
ProtocolSCTP/TCP/UDP
Serviceftp
ReferenceRFC 959, RFC 9260
Modified2022-02-07

Frequently asked questions

What is port 21 used for?

Port 21 is registered with the IANA for ftp (SCTP/TCP/UDP). Description: File Transfer Protocol [Control]; FTP.

Is port 21 a well-known port?

Yes. Port 21 is in the range 0–1023 (system or well-known ports). On Linux and macOS only privileged processes may bind to these ports.

How do I check whether port 21 is open?

Locally on Linux with ss -tulpn | grep ':21\b', on Windows with netstat -ano | findstr :21. To test a remote host use Test-NetConnection <host> -Port 21 in PowerShell or nc -zv <host> 21 on Linux/macOS.

How do I open port 21 in the firewall?

Ubuntu/Debian (ufw): sudo ufw allow 21/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=21/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 21" -Direction Inbound -Protocol TCP -LocalPort 21 -Action Allow.

IANA registry entries

ProtocolServiceDescription (IANA)
TCPftpFile Transfer Protocol [Control]
UDPftpFile Transfer Protocol [Control]
SCTPftpFTP

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