LinuxHostingSupport

The default firewall of Linux is iptables which can be use to block Ftp access/port on your server. If you have a CSF firewall (which also use iptables), see section 2.

Section 1:  Iptables

Completely block Ftp access on the server:

# iptables -A INPUT -p tcp --dport 21 -j DROP

Block Ftp access for a specific IP address, say 11.12.13.14

# iptables -A INPUT -p tcp -s 11.12.13.14 --dport 21 -j DROP

Block Ftp access for a specific subnet

# iptables -I INPUT -p tcp -s 11.12.13.0/24 --dport 21 -j DROP

The rules need to be saved else they will be removed if the iptables service is restarted.

# service iptables save

Section 2: CSF

To completely block Ftp access, edit csf.conf file and remove port 21 from the TCP_IN list

# pico /etc/csf/csf.conf

To block Ftp access for a specific IP address, edit the csf.deny file

# pico /etc/csf/csf.deny

and place the following line

tcp:in:d=21:s=11.12.13.14

Save the file and don’t forget to restart the firewall.