CentOS7.4 关闭firewall防火墙，改用iptables

1.关闭默认的firewall防火墙

systemctl stop firewalld.service #停止firewall
systemctl disable firewalld.service #禁止firewall开机启动
firewall-cmd --state #查看默认防火墙状态（关闭后显示notrunning，开启后显示running）

2.开启iptables

yum install iptables （根据centOS7的版本和内核，有些版本已经装过，可以跳过此命令）
yum install iptables-services
service iptables restart
chkconfig iptables on或者systemctl enable iptables.service开机自启

3.编辑防火墙文件（开启了21,22,80,3306端口）
vim /etc/sysconfig/iptables
 

# sampleconfiguration for iptables service 
# # you can edit thismanually or use system-config-firewall 
# # please do not askus to add additional ports/services to this default configuration 
*filter 
:INPUT ACCEPT [0:0] 
:FORWARD ACCEPT [0:0] 
:OUTPUT ACCEPT [0:0] 
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A INPUT -p icmp -j ACCEPT 
-A INPUT -i lo -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m tcp --dport 3306 -j ACCEPT 
-A INPUT -j REJECT --reject-with icmp-host-prohibited 
-A FORWARD -j REJECT --reject-with icmp-host-prohibited 
COMMIT 

5.查看本机关于IPTABLES的设置情况

iptables -L -n