IPTABLES and ports

 How to restrict MySQL port access (a2hosting.com)

ou can use iptables to create firewall rules that restrict access to port 3306. The advantage of this method is that you can selectively grant or deny access to port 3306 based on IP addresses or other criteria.

For example, to block external access to port 3306 completely, type the following command:

iptables -A INPUT -p tcp --dport 3306 -j DROP

Similarly, to grant access to a specific IP address and block all others, type the following commands. Replace xxx.xxx.xxx.xxx with the IP address for which you want to grant access:

iptables -A INPUT -p tcp --dport 3306 -s xxx.xxx.xxx.xxx -j ACCEPT
iptables -A INPUT -p tcp --dport 3306 -j DROP

You can grant MySQL access to additional IP addresses by inserting rules in the INPUT chain before the DROP rule. For example:

iptables -I INPUT 1 -p tcp --dport 3306 -s xxx.xxx.xxx.xxx -j ACCEPT
Task: Open port 3306
In most cases following simple rule opens TCP port 3306:
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 3306 -j ACCEPT
The following iptable rules allows incoming client request (open port 3306) for server IP address 202.54.1.20. Add rules to your iptables shell script:
iptables -A INPUT -p tcp -s 0/0 --sport 1024:65535 -d 202.54.1.20 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 3306 -d 0/0 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
However in real life you do not wish give access to everyone. For example in a web hosting company, you need to gives access to MySQL database server from web server only. Following example allows MySQL database server access (202.54.1.20) from Apache web server (202.54.1.50) only:
iptables -A INPUT -p tcp -s 202.54.1.50 --sport 1024:65535 -d 202.54.1.20 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 3306 -d 202.54.1.50 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
Please note if you follow above setup, then you need tell all your hosting customer to use 202.54.1.50 as MySQL host in PHP/Perl code. A better approach is to create following entry in /etc/hosts file or use fully qualified domain name (create dns entry) mysql.hostingservicecompany.com which points to 202.54.1.50 ip:
202.54.1.50 mysql
In shot MySQL database connection code from PHP hosted on our separate webserver would look like as follows:
// ** MySQL settings ** //
define('DB_NAME', 'YOUR-DATABASE-NAME');     // The name of the database
define('DB_USER', 'YOUR-USER-NAME');     // Your MySQL username
define('DB_PASSWORD', 'YOUR-PASSWORD''); // ...and password
define('DB_HOST', 'mysql');       // mysql i.e. 202.54.1.50
// ** rest of PHP code ** //
Task: Allow outgoing MySQL request on TCP port 3306
Even you can allow outgoing MySql client request (made via mysql command line client or perl/php script), from firewall host 202.54.1.20 as follows:
iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 1024:65535 -d 0/0 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 0/0 --sport 3306 -d 202.54.1.20 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT