[root@localhost ~]# yum install iptables -y
[root@localhost ~]# yum install iptables-services

查看安装情况

[root@localhost ~]# rpm -qa|grep iptables
iptables-1.4.21-24.1.el7_5.x86_64
iptables-services-1.4.21-24.1.el7_5.x86_64
修改配置文件

[root@localhost ~]# vi /etc/sysconfig/iptables

#firewall configuration written by system-config-firewall
# Manual customization of this file is not recommended.

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 3306 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

保存退出

[root@localhost ~]#systemctl start iptables.service

启动正常，安装成功。

[root@localhost ~]# systemctl enable iptables
[root@localhost ~]# iptables -nv -L --line-number  //查看IP规则 ,--line-number 标上序号