修改防火墙配置文件：
vi /etc/sysconfig/iptables
增加下面一行：
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 3306 -j ACCEPT
如果想开通21等端口，只需要将3306换成21等要开放的端口就可以了。
配置后，重新启动iptable
service iptables restart
这时就可以从其他机器访问Mysql了。
注意：
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 3306 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
是拒绝icmp访问，对于其它的报文返回一个主机禁止访问的错误
开通3306 端口的行必须在icmp-host-prohibited前
Open port 80
Open flle /etc/sysconfig/iptables:# vi /etc/sysconfig/iptables
Append rule as follows:-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
Save and close the file. Restart iptables:# /etc/init.d/iptables restart
Open port 110
Append rule as follows:-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 110 -j ACCEPT
Open port 143
Append rule as follows:-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 143 -j ACCEPT
Restart iptables service
Type the following command:# service iptables restart
Verify that port is open
Run following command:netstat -tulpn | less
Make sure iptables is allowing port 80 / 110 / 143 connections:iptables -L -n
Refer to iptables man page for more information about iptables usage and syntax:man iptables