你可以用rpm -qa | grep iptables来查看，centos7默认防火墙是firewalld，iptables应该是没有安装，你可以用yum install iptables -y来安装。

1、关闭firewall：
systemctl stop firewalld.service #停止firewall
systemctl disable firewalld.service #禁止firewall开机启动

2、安装iptables防火墙
yum install iptables-services #安装

3

接下来的事情就和用iptables是一样的了，若要开启某端口，则（80端口为例，红色为添加的规则）（有先后顺序）：
vi /etc/sysconfig/iptables
-A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT #允许80端口通过防火墙

############################## 添加后 防火墙规则如下所示 ##############################
# 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 -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

重启服务 

 
 

  
  

 
 
systemctlrestartiptables

systemctl enable iptables.service#设置防火墙开机启动