iptable是Linux自带的防火墙。CentOS系统镜像安装后默认没有开放80端口，如何编辑 iptable 规则来实现添加/删除。
查看当前iptable防火墙规则
# iptables -L -n
编辑规则
# vi /etc/sysconfig/iptables
出现如下（例子，部分会略有不同，只是讲述大概方法）：
# 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 -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
我们可以在22端口下添加80端口，如（按键盘 I 进入编辑模式）：
-A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
以上例完成后完整的应该是：
# 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
按键盘Esc退出编辑模式，按Shift+:输入x回车，退出并保存。然后重启iptable使规则生效：
#service iptables restart
