CentOS 7.0默认使用的是firewall作为防火墙，这里改为iptables防火墙。
1、关闭firewall：
#停止firewall
systemctl stop firewalld.service
#禁止firewall开机启动
systemctl disable firewalld.service
#移除firewall
yum remove firewalld
2、安装iptables防火墙
#安装
yum install iptables-services
#编辑防火墙配置文件
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
################################################################################
:wq! #保存退出
#最后重启防火墙使配置生效
systemctl restart iptables.service
#设置防火墙开机启动
systemctl enable iptables.service