RHEL7 FTP server error: ftp: connect: No route to host solution

When setting up FTP server on Redhat 7 Linux box the following error message ftp: connect: No route to host may pop-up during FTP client session:

230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
227 Entering Passive Mode (10,1,1,110,138,70).
ftp: connect: No route to host
ftp> 

The cause of the above error is a missing ip_conntrack_ftp kernel module. Quick fix solution is to load this module using modprobe:

# modprobe ip_conntrack_ftp

However, you will need to do this every time you reboot your RedHat server. Thus as a more permanent solution you can persistently load this module after each reboot by creating executable shell script within /etc/sysconfig/modules/ directory. Create file /etc/sysconfig/modules/iptables.modules with the following content:

#!/bin/sh
exec /sbin/modprobe ip_conntrack_ftp >/dev/null 2>&1

Once you save this file you also need to make it executable:

# chmod +x /etc/sysconfig/modules/iptables.modules

The above script will load the following modules after each reboot:

[root@rhel7 ~]# lsmod | grep ftp
nf_conntrack_ftp       18638  0 
nf_conntrack          101024  9 nf_nat,nf_nat_ipv4,nf_nat_ipv6,xt_conntrack,ip6table_nat,nf_conntrack_ftp,iptable_nat,nf_conntrack_ipv4,nf_conntrack_ipv6