Recently I had the challenge, that the MySQL database of one of the Magento shops I maintain wasn’t accessible directly through the Net. The access was restricted to the Webserver only. So I had to tunnel MySQL through SSH. And that worked like that:

• edit the ssh config (~/.ssh/config) on the remote Webserver

  Host *
    ForwardAgent yes

• create  a port mapping through ssh (the local port 3307 is mapped to the MySQL standard port of the webserver)

  $> ssh -L 3307:localhost:3306 user@server.com

• Add your key to the server to gain passwordless access to the Webserver
• Now you can use the remote MySQL database in you local Magento installation as if it would be located on the local environment.

  <host><![CDATA[127.0.0.1]]></host>
  <port><![CDATA[3307]]></port>
  <username><![CDATA[username]]></username>
  <password><![CDATA[password]]></password>
  <dbname><![CDATA[database]]></dbname>
  <!-- ... -->

  Naturally you can use this port mapping als with other MySQL driven applications or clients.

That’s it. This was how I tunnel MySQL through SSH if required.