Port 21: FTP
The FTP control connection for logins and commands. A constant target of password guessing, and unencrypted. Replace with SFTP, or use FTPS and restrict who can connect.
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Port Lookup
Port 21 at a glance
Port21
ProtocolTCP
ServiceFTP
Open to the Internet?Only to addresses that need it
See What Is Listeningss -lntup | grep ':21 '
Test From Outsidenc -zv your-server 21
Block with UFWufw deny 21/tcp
Block with nftablesnft add rule inet filter input tcp dport 21 drop
FTP uses TCP port 21. The FTP control connection for logins and commands.
A constant target of password guessing, and unencrypted. Replace with SFTP, or use FTPS and restrict who can connect.
Allow port 21 only from the addresses that need it: your office, a VPN or a bastion host. The firewall rule generator builds those rules for nftables, iptables and UFW.
Other Ports
20 FTP Data21 FTP22 SSH23 Telnet25 SMTP53 DNS67 DHCP Server80 HTTP110 POP3123 NTP143 IMAP161 SNMP389 LDAP443 HTTPS445 SMB465 SMTPS514 Syslog587 Mail Submission853 DNS over TLS993 IMAPS995 POP3S1194 OpenVPN1433 Microsoft SQL Server1900 SSDP / UPnP2049 NFS2083 cPanel (SSL)2087 WHM (SSL)3306 MySQL / MariaDB3389 RDP3478 STUN / TURN5060 SIP5432 PostgreSQL5900 VNC6379 Redis8006 Proxmox VE8080 HTTP Alternate8443 HTTPS Alternate11211 Memcached25565 Minecraft27017 MongoDB51820 WireGuard
Questions
What is port 21 used for?
FTP. The FTP control connection for logins and commands.
Is it safe to open port 21?
Only to addresses that need it. A constant target of password guessing, and unencrypted. Replace with SFTP, or use FTPS and restrict who can connect.
How do I check if port 21 is open?
On the server, ss -lntup | grep ':21 ' shows what is listening. From another machine, nc -zv your-server 21 shows whether the firewall lets it through.
How do I block port 21?
With UFW: ufw deny 21/tcp. With nftables, add a drop rule for dport 21 in your input chain.
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