打開iptables的配置文件：
vi /etc/sysconfig/iptables
修改CentOS防火牆時注意：一定要給自己留好後路,留VNC一個管理端口和SSh的管理端口
下面是一個iptables的示例：
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp –icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 53 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m udp -p udp –dport 53 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 25 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT –reject-with icmp-host-prohibited
COMMIT
修改CentOS防火牆需要注意的是，你必須根據自己服務器的情況來修改這個文件。
舉例來說，如果你不希望開放80端口提供web服務，那麼應該相應的刪除這一行：
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 80 -j ACCEPT
全部修改完之後重啟iptables:
service iptables restart
你可以驗證一下是否規則都已經生效：iptables -L
這樣，我們就完成了CentOS防火牆的設置修改。
