例如：CentOS6.5开启3306端口。
输入命令：
vi /etc/sysconfig/iptables
内容修改成如下：
# 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
输入命令 ctrl+c
输入命令 ：wq (冒号也要输入)
*****************************************扩展************************************************************
如果测试socket连接，需要再打开一个窗口，那就直接增加一个端口号。
-A INPUT -m state state NEW -m tcp -p tcp dport 23000 -j ACCEPT
增加完之后需要重启服务：
sudo service iptables restart
重启之后查看端口号打开状态：使用命令
/etc/init.d/iptables status
