[root@anon ~]# iptables -A INPUT -p tcp --dport 21 -j ACCEPT
[root@anon ~]# iptables -A OUTPUT -p tcp --sport 20 -j ACCEPT
[root@anon ~]# service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[  OK  ]
[root@anon ~]# systemctl stop vsftpd
[root@anon ~]# systemctl restart iptables
[root@anon ~]# systemctl start vsftpd
[root@anon ~]# systemctl status vsftpd
● vsftpd.service - Vsftpd ftp daemon
   Loaded: loaded (/usr/lib/systemd/system/vsftpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2019-07-12 20:33:17 UTC; 7s ago
  Process: 878 ExecStart=/usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf (code=exited, status=0/SUCCESS)
 Main PID: 879 (vsftpd)
   CGroup: /system.slice/vsftpd.service
           └─879 /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf

Jul 12 20:33:17 anon systemd[1]: Starting Vsftpd ftp daemon...
Jul 12 20:33:17 anon systemd[1]: Started Vsftpd ftp daemon.
[root@anon ~]# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ftp

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:ftp-data