All ports
Port21/SCTP
ftpPort
21
Protocol
SCTP
Category
Well-Known
Service
ftp
What is port 21?
Port 21/SCTP is a Well-Known port, assigned by IANA for widely recognized services. It is associated with the ftp service.
FTP
Useful commands
nmapnmap -p 21 -sV example.comnetcatnc -zv example.com 21curlcurl -v http://example.com:21/telnettelnet example.com 21bash(echo > /dev/sctp/example.com/21) 2>/dev/nullFirewall commands
UFWAllow
sudo ufw allow 21/sctpDeny
sudo ufw deny 21/sctpiptablesAllow
sudo iptables -A INPUT -p sctp --dport 21 -j ACCEPTDeny
sudo iptables -D INPUT -p sctp --dport 21 -j ACCEPTfirewalldAllow
sudo firewall-cmd --permanent --add-port=21/sctpWindowsAllow
netsh advfirewall firewall add rule name="Open Port 21" dir=in action=allow protocol=SCTP localport=21Security Risks
- Unauthorized access to the service
- Data exposure if the service is unauthenticated
- Outdated versions with vulnerabilities
- Incorrect service configuration
Frequently Asked Questions
What service runs on port 21/SCTP?
Port 21/SCTP is associated with the ftp service. FTP
Is it safe to expose port 21 to the Internet?
It depends on the service and configuration. Port 21 (ftp) is a Well-Known port. If you need to expose it, keep the service updated, use strong authentication, and configure a firewall. It's always recommended to restrict access by IP when possible.
How do I check if port 21 is open?
You can use nmap: `nmap -p 21 -sV example.com`, netcat: `nc -zv example.com 21`, or the bash command: `(echo > /dev/sctp/example.com/21) 2>/dev/null && echo "Open" || echo "Closed"`.
How do I open or close port 21 on my firewall?
On Linux with UFW: `sudo ufw allow 21/sctp` (open) or `sudo ufw deny 21/sctp` (close). With iptables: `sudo iptables -A INPUT -p sctp --dport 21 -j ACCEPT`. On Windows: `netsh advfirewall firewall add rule name="Open Port 21" dir=in action=allow protocol=SCTP localport=21`.
What applications and services use port 21?
Port 21/SCTP is used by the ftp service. Specific uses depend on the software and configuration. Check our related tools section for more information.