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