Often you do not have direct access to a desired
server, because a firewall blocks the port or you are on another
network than the server. But eventually you may have access to a proxy
server, from which you can access the desired server. For example you
would like to access an Oracle database on
192.168.151.2 on port 1521 with
you local SQL tools and you don't want to do it from the proxy
server. With SSH port forwarding you can establish a
logical connection through the proxy an
you will then be able to access the Oracle database through it.
You can use the very common SSH client PUTTY to
establish this logical connection
Port Forwarding using SSH
In order to use port forwarding to
connect from your local machine to a port on a remote server, you need
Choose a port number on your local
machine (e.g. 5500) where PuTTY should listen for incoming connections.
Now, before you start your SSH
connection, go to the PuTTY Tunnels panel. Make sure the «Local» radio
button is set. Enter the local port (e.g. 5500) number into the «Source
port» box. Enter the destination host name and port number into the
«Destination» box, separated by a colon (e.g. 192.168.151.2:1521).
Now click the [Add] button. The
details of your port forwarding should appear in the list box.
Now start your session and log in
to the proxy host. To check that PuTTY has set up the port forwarding
correctly, you can look at the PuTTY Event Log.
Now if you connect to the source
port number on your local PC, you should find that it answers you
exactly as if it were the service running on the destination machine.
You can also forward ports in the
other direction: arrange for a particular port number on the server
machine to be forwarded back to your PC as a connection to a service on
your PC or near it. To do this, just select the «Remote» radio button
instead of the «Local» one. The «Source port» box will now specify a
port number on the server.
Enter Source and Destination, then click Add Button
After clicking the Add Button
If you need to start a graphical application from the
database server (on 192.168.151.2) and the
output should be displayed on your local PC, then you must activate X11
forwarding in PUTTY.
Now log in to the SSH proxy server as normal. To check
that X forwarding has been successfully negotiated during connection
startup, you can check the PuTTY Event Log.
From the proxy server you must now enable X11
forwarding to the DB server, this can be established with the -X option
proxy> ssh -X email@example.com
Now you can start for example Oracle's
runInstaller and the output is displayed
on your local PC - do not forget to start the cygwin X11 server on the